Longevity Glossary

17α-Estradiol is a mirror-image form of the main estrogen, 17β-estradiol. The technical word is a 'stereoisomer'. But it has far weaker feminizing effects. So it barely acts like…

8-OHdG is a chemically damaged DNA building block, formed when reactive oxygen species (ROS) attack a specific spot on the guanine base. It is one of the most common and…

AAA screening uses a single bedside abdominal ultrasound to measure the widest part of your infrarenal aorta. An abdominal aortic aneurysm (AAA) is defined as 3 cm or more. The…

AAV gene therapy uses a re-engineered virus (adeno-associated virus, AAV) to deliver a working gene into your tissues. The cargo is a 'transgene cassette': usually a promoter, a…

Absolute risk (AR) is the probability that you experience an event, like a heart attack, a cancer diagnosis, or death, within a defined time period. Relative risk (RR) expresses…

Acarbose is an 'alpha-glucosidase inhibitor', approved for type 2 diabetes. It works in your gut: by blocking the breakdown of carbohydrates, it blunts the spikes in blood…

The ACE insertion/deletion (I/D) polymorphism (rs4646994) is a 287-base-pair stretch of DNA (an Alu repeat). It is either present or absent in intron 16 of the ACE gene. The D…

Actigraphy uses a wrist-worn motion sensor (accelerometer) to estimate your sleep and wake. It reads your movement patterns over days to weeks. It is a low-burden, take-home…

Adenosine is a small molecule (a purine nucleoside) that builds up in your brain while you are awake, as a byproduct of neurons using energy. It acts on receptors (A1 and A2A) to…

Adiponectin is a hormone your fat cells release (an 'adipokine'), mostly from white fat. It is unusual among fat hormones: it goes DOWN as you gain fat, not up. Levels fall with…

Adult hippocampal neurogenesis (AHN) is how new neurons are born from neural stem and progenitor cells. They form in the subgranular zone of the hippocampal dentate gyrus (DG),…

Adult stem cells (also called somatic stem cells) are undifferentiated cells that live in specific tissue 'niches'. Their job is to maintain and repair that tissue throughout…

Advanced glycation end-products (AGEs) are stable, often crosslinked compounds. They form when sugars react with your proteins, lipids, or DNA over time. They build up in…

Aerobic capacity is the most oxygen your body can take in and use to make ATP during long exercise. By the Fick principle (VO2 = Q × (a-v)O2), it depends on two things: how well…

The AGE-RAGE axis is an inflammation-driving signaling loop. It starts when advanced glycation end products (AGEs), and other ligands, bind a receptor called RAGE (coded by the…

Akkermansia muciniphila is a Gram-negative gut bacterium that eats mucin and lives in your intestinal mucus layer. It is usually a small share of a healthy microbiome (under 1%…

Albumin is the most abundant protein in your blood plasma, made only by your liver. It keeps fluid inside your blood vessels (colloid osmotic pressure) and ferries hormones,…

The albumin/globulin (A/G) ratio compares two groups of proteins in your blood. It is calculated as albumin divided by (total protein minus albumin). The 'globulin' part includes…

Alcohol (ethanol) is a confirmed human carcinogen (Group 1). And chronic drinking speeds up your biological aging through several mechanisms. Your body oxidizes ethanol into…

Alkaline phosphatase (ALP) is an enzyme that snips phosphate groups in an alkaline environment. The level in your blood is a mix of forms from several organs, mainly your liver,…

Allostatic load is the cumulative wear and tear your body racks up from adapting to chronic stress. Here is the idea. Your systems keep adjusting to keep you stable, a process…

Alpha-lipoic acid (ALA) is a sulfur-containing fatty acid. It is an essential helper (cofactor) for two mitochondrial enzyme complexes (pyruvate dehydrogenase and α-ketoglutarate…

ALT (alanine aminotransferase) and AST (aspartate aminotransferase) are enzymes inside your cells that spill into your blood when liver cells are injured. ALT is fairly…

AMPK is your cell's low-fuel warning light. Its full name is AMP-activated protein kinase, and it switches on when energy runs low, when AMP and ADP rise relative to ATP (the…

Amyloid-β (Aβ) is a family of small protein fragments, 36 to 43 amino acids long. They are snipped out of a bigger protein (amyloid precursor protein, APP) by two enzymes (β- and…

Anabolic resistance is the age-related blunting of muscle protein synthesis (MPS) in response to protein and resistance exercise. In young adults, roughly 20 to 25 g of protein…

The anaerobic threshold (AT) is the exercise intensity above which your aerobic system cannot keep up with the energy demand, so lactate starts building faster than your body…

Angiogenesis is the growth of new blood vessels from existing capillaries. The main driver is VEGF-A (vascular endothelial growth factor-A), a protein that binds two receptors…

Antagonistic pleiotropy is an idea from evolutionary biologist George C. Williams, dating to 1957. Here is the idea. A gene that helps you early in life can harm you later, after…

Apigenin is a plant flavone, found in parsley, celery, chamomile, and dried oregano. In a 2013 Diabetes paper, Escande and colleagues found that apigenin inhibits CD38, an enzyme…

Apolipoprotein A-I (ApoA-I) is the main protein of 'good' HDL cholesterol. Your liver and gut make it, and it makes up about 70% of HDL's protein. It switches on an enzyme (LCAT)…

Apolipoprotein B (ApoB) is the backbone protein of the 'bad' lipoproteins that clog arteries. These include LDL, VLDL, IDL, and Lp(a). Each such particle carries about one…

Apolipoprotein E (APOE) is a fat-transport protein, coded by the APOE gene. The gene comes in three versions (alleles): ε2, ε3, and ε4, giving six possible genotypes. The ε4…

The APOE ε4 allele is a gene variant that makes the E4 form of apolipoprotein E. It differs from the common ε3 form by a single building block at position 112 (cysteine swapped…

Apoptosis is a tightly controlled form of programmed cell death. The cell is taken apart in an orderly way, by enzymes called caspases. It usually does not spark inflammation,…

Amyloid precursor protein (APP) is a membrane-spanning protein. It is coded on chromosome 21 and found widely in your brain and nerves. How it is cut decides everything. There…

Low-dose aspirin (usually 75 to 100 mg a day) permanently blocks an enzyme (COX-1) in your platelets. That cuts their production of thromboxane A2 and makes them less likely to…

The AST/ALT ratio (also called the De Ritis ratio, after Fernando De Ritis, who described it in the 1950s) is just one liver enzyme divided by another: AST divided by ALT. In…

Astaxanthin is a red-pink pigment (a ketocarotenoid). It is made mainly by a microalga (Haematococcus pluvialis). It then travels up the food chain into crustaceans, salmon, and…

Atherosclerosis is the slow, inflammation-driven clogging of your medium and large arteries. It starts when cholesterol-carrying particles (ApoB-containing lipoproteins, mainly…

ATM (short for ataxia-telangiectasia mutated) is a gene that makes a protein kinase. That kinase is the master alarm for one of the worst kinds of DNA damage: a double-strand…

The autonomic nervous system (ANS) runs all the things you do not consciously control: heart rate, blood pressure, digestion, breathing. It has two main branches. The sympathetic…

Autophagy is your body's recycling program for worn-out cell parts. The name means "self-eating": a cell wraps damaged proteins and broken organelles in a double-membrane bag (an…

B-cell senescence covers the age-related changes in your B cells (the antibody-making immune cells) that weaken your antibody immunity. A hallmark is the buildup of…

The Bacteroidetes/Firmicutes ratio was prominently proposed in the mid-2000s as a marker of your gut microbiome's health. It came from observations in obese mice and small human…

Baroreflex sensitivity (BRS) measures how strongly your heart rate responds to quick changes in blood pressure. It is given as milliseconds of change in the gap between beats,…

BDNF (brain-derived neurotrophic factor) is a growth-factor protein. It supports neuron survival, the formation of synapses, and (at least in animals) the birth of new neurons in…

Beclin-1 (made by the BECN1 gene) is a core part of the machinery that starts autophagy in your cells. It belongs to a complex (the class III PI3K, or VPS34, complex) that…

Berberine is an isoquinoline alkaloid, found in several plant groups, including Berberis, goldenseal (Hydrastis canadensis), and Coptis chinensis. It is sold as a dietary…

Bifidobacterium is a genus of Gram-positive, anaerobic, branched-rod bacteria, in the phylum Actinobacteria. It is one of the first colonizers of a baby's gut, especially in…

Bile acids begin as digestion helpers. But they double as powerful signals, and your gut bacteria reshape them. Your liver makes the 'primary' ones from cholesterol. There are…

Bilirubin is the yellow waste your body makes when it recycles old red blood cells. It travels in two forms. First it rides on a protein (albumin) as 'unconjugated', or indirect,…

Biological age is an estimate of how old your body seems to be. It is based on physiological and molecular markers, not on the calendar. You can derive it several ways. Options…

Biomolecular condensates are membraneless 'organelles' that form by liquid-liquid phase separation (LLPS). That is the spontaneous demixing of proteins and RNAs into a dense…

Bisphosphonates are bone drugs that copy a natural molecule (pyrophosphate) and stick tightly to the mineral in your bones. When bone-dissolving cells (osteoclasts) chew on that…

Blood flow restriction (BFR) training puts a pneumatic cuff or elastic wrap near the top of a limb. It partially blocks the blood leaving the limb (venous return) while still…

The blood-brain barrier (BBB) is a tightly controlled wall between your bloodstream and your brain. It is built from specialized endothelial cells lining the brain's capillaries,…

Blue Zones are regions reported to have unusually many centenarians. The popular list (from Buettner) includes Okinawa (Japan), Sardinia (Italy), Nicoya (Costa Rica), Ikaria…

Bone mineral density (BMD) is the amount of mineral, mostly hydroxyapatite, packed into your bone, per unit area (g/cm²) or volume. It is most often measured at your lumbar spine…

Box breathing is a paced breathing technique. You use four equal-length phases: inhale, hold, exhale, and hold (commonly four seconds each). Slowing your breathing well below the…

BPC-157 is a synthetic 15-amino-acid peptide. It is based on a sequence found in human gastric juice. It is marketed for healing your tendons, ligaments, and gut. Animal studies…

MRI-based brain age estimates how old your brain looks biologically, from brain-imaging features. Those features include cortical thickness, white-matter integrity, gray-matter…

Brain MRI volumetrics uses structural MRI to measure the size of specific brain regions. The usual targets are the hippocampus, the fluid-filled ventricles, and total gray and…

The branched-chain amino acids (BCAAs) are leucine, isoleucine, and valine. They are essential amino acids, rich in meat, dairy, eggs, and the protein supplements you might buy.…

Brown adipose tissue (BAT) is your body's heat-generating fat. It is packed with mitochondria and a protein called UCP1. UCP1 lets the mitochondria release energy as heat instead…

Butyrate is a four-carbon short-chain fatty acid (SCFA), made in your colon when anaerobic bacteria ferment dietary fiber. The main producers are Faecalibacterium prausnitzii and…

C-peptide is a 31-amino-acid chain. It is cut out of proinsulin inside your pancreatic beta cells. One C-peptide is released for every insulin molecule. So your fasting C-peptide…

CA-125 (cancer antigen 125) is a large mucin-like protein made by the MUC16 gene. It sits on certain body-cavity and reproductive-tract surfaces. It sheds into your blood when…

Caffeine is a methylxanthine alkaloid, found in coffee, tea, and cocoa. It works by blocking your adenosine A1 and A2A receptors. Normally, adenosine signaling makes you drowsy…

Caloric restriction is a sustained cut in your energy intake. Typically that is 10 to 30% below eating freely (ad libitum), but without malnutrition. It switches on conserved…

A caloric restriction mimetic (CR mimetic) copies some effects of eating less, without you having to cut calories long-term. What effects? It activates AMPK and sirtuins. It…

Canakinumab (Ilaris, from Novartis) is a fully human antibody. It neutralizes the inflammatory signal interleukin-1β (IL-1β) in your body. The FDA approved it in 2009 for a rare…

Cardiac MRI (CMR) is the gold standard for measuring how well your heart pumps. It quantifies the volumes of the left and right ventricles. It also measures the ejection fraction…

Cardiac output (Q) is the volume of blood your heart pumps per minute. It equals heart rate (HR, beats per minute) times stroke volume (SV, mL per beat). At rest, Q is 4 to 6…

Cardiolipin (CL) is a special double phospholipid. It is found almost only in the inner membrane of your mitochondria. It makes up roughly 15 to 20% of that membrane's lipid. Its…

Cardiorespiratory fitness (CRF) is how well your heart, blood vessels, and lungs deliver oxygen to your muscles during sustained activity. It is most often measured as VO2max.…

Carnosine is a dipeptide (beta-alanine plus L-histidine), concentrated in your skeletal muscle and nerve tissue. It works through four mechanisms. It buffers pH inside cells…

Carotid intima-media thickness (CIMT) is an ultrasound measurement of the combined thickness of the two inner layers (intima and media) of your carotid artery wall. It acts as a…

Cathepsins are a family of protein-chewing enzymes (proteases) that work inside your lysosomes, the cell's acidic recycling chambers. Most are cysteine proteases (cathepsins B,…

CausAge is an epigenetic clock built to fix a deep flaw in the clocks that estimate your biological age. It was introduced by Ying, Gladyshev and colleagues (preprint 2022;…

CD38 is a membrane glycoprotein with two enzyme jobs: it breaks down NAD+ and it cyclizes ADP-ribose. It shows up on many cells, but most heavily on immune cells. It splits NAD+…

The CD4/CD8 ratio compares two kinds of T cell in your blood: CD4+ helper T cells versus CD8+ killer T cells. A healthy ratio is usually cited as about 1.5 to 2.5. In young,…

Cellular reprogramming is the lab process of converting one cell type into another. Most often, it turns a specialized body cell back into a pluripotent stem cell. It does this…

Cellular senescence is what happens when a cell stops dividing for good but refuses to die. Stress sets it off: DNA damage, frayed telomeres, a switched-on cancer gene, or…

A centenarian is a person who has reached the age of 100 or more. Centenarians are a key research group in longevity research. Why? Because they tend to delay or escape the major…

When scientists study people who reach extreme old age, they keep finding a different gut microbiome. Two studies stand out. An Italian group (Biagi and Franceschi) looked at…

Cerebral blood flow (CBF) is how much blood your brain gets per minute, measured in mL per 100 g of tissue per minute. Three systems regulate it: autoregulation, sensitivity to…

Cerebral small vessel disease (CSVD) is damage to your brain's tiniest blood vessels: the small arteries, arterioles, capillaries, and venules. It shows up on brain scans as a…

Cerebrolysin is a peptide preparation derived from pig brain. It is made by EVER Pharma (Austria). It contains small neuropeptides and free amino acids. It is marketed for your…

CETP (cholesteryl ester transfer protein) swaps cholesteryl esters out of HDL for triglycerides from VLDL and LDL, which effectively lowers your HDL cholesterol. The I405V…

Cell-free DNA (cfDNA) is short fragments of DNA floating in your blood plasma. They are released by cells that die, by apoptosis or necrosis. (The fragments are typically 140-200…

The cGAS-STING pathway is one of your cells' built-in alarms for danger DNA. The sensor, cGAS (cyclic GMP-AMP synthase), detects double-stranded DNA floating loose in the cell's…

Chaperone-mediated autophagy (CMA) is a precise way your cells recycle individual proteins. Unlike bulk autophagy, it does not wrap cargo in a vesicle. Instead, it ferries one…

Choline is a water-soluble nutrient. The US Institute of Medicine officially recognized it as essential in 1998. It set Adequate Intakes of 425 mg a day for adult women and 550…

Christensenella minuta is a strictly anaerobic gut bacterium, in the Christensenellaceae family. In the TwinsUK study, Goodrich and colleagues (2014) made a key find. It is the…

Chromatin is the bundle of DNA, histone proteins, and other proteins that packs your genome into the nucleus. Its basic unit is the nucleosome. It can be packed tight (as…

Chronic psychological stress is a sustained sense of threat or demand that keeps your stress system (the HPA axis) switched on. That means your cortisol stays high for long…

Chronological age is simply the time since you were born, usually counted in years. It is the standard reference in demography, medicine, and epidemiology, and it is still one of…

Chronotype is your individual leaning toward earlier or later sleep-wake timing. It is commonly described as a morning type, an intermediate type, or an evening type. It is…

Your circadian rhythm is the body's roughly 24-hour internal clock. It coordinates when you sleep and wake, when hormones release, and your body temperature and metabolism. It is…

Clonal hematopoiesis of indeterminate potential (CHIP) means one blood stem cell, carrying a driver mutation, has quietly expanded into a large clone. The usual mutated genes are…

Cytomegalovirus (CMV) is a very common beta-herpesvirus that sets up lifelong latency after the first infection. Seroprevalence runs from about 40 to 70% in high-income…

Coenzyme Q10 (also called ubiquinone) is a fat-soluble molecule. It is essential for mitochondrial electron transport and ATP production, and it acts as an antioxidant inside…

Cognitive reserve is your brain's functional adaptability. Yaakov Stern developed and formalized the concept. He built on earlier 'brain reserve' work by Katzman and colleagues…

Colchicine is a plant alkaloid from the autumn crocus (Colchicum autumnale). It fights inflammation by binding tubulin and disrupting microtubules. That hampers neutrophil…

Cold exposure is the deliberate use of cold air, water, or ice as a hormetic stressor. Think cold showers, ice baths, or cryotherapy. Acute cold triggers a release of…

Cold thermogenesis is how your body makes heat when it gets cold. It comes in two forms. One is shivering, where your muscles generate heat. The other is non-shivering, driven by…

Collagen peptides are also called hydrolysed collagen or collagen hydrolysate. They are made by enzymatically breaking down animal collagen into small fragments, about 2 to 5…

The complement system is a squad of more than 30 blood and cell-surface proteins that form a fast-acting arm of your innate immune system. It switches on through three routes…

Compression of morbidity is a concept introduced by James Fries in 1980. It describes a scenario where the onset of chronic disease and disability is pushed back faster than…

The interference effect is the way endurance training can blunt your gains from resistance training, especially strength, power, and muscle growth (hypertrophy), when you do both…

Confounding is when a third variable distorts the apparent link between an exposure and an outcome. That third variable is the confounder. It is independently tied to both the…

A continuous glucose monitor (CGM) is a wearable sensor that tracks your blood sugar around the clock. It usually sits just under your skin and reads interstitial glucose every…

The coronary artery calcium (CAC) score comes from a non-contrast cardiac CT scan. It is reported as an 'Agatston score'. It measures how much calcified plaque is in your…

Coronary CT angiography (CCTA) is a CT scan that, with an iodine contrast dye in your vein, builds a 3D picture of your heart's arteries. It shows both how narrow an artery is…

Cortisol is the main glucocorticoid (stress hormone) from your adrenal glands. It is the final output of the HPA axis, the loop linking your hypothalamus, pituitary, and…

The cortisol awakening response (CAR) is a sharp rise in your salivary cortisol right after you wake up. On average it climbs about 50% (commonly reported between roughly 38 and…

Creatine is a compound your body makes in the liver and kidneys. It builds it from the amino acids arginine, glycine, and methionine. You also get creatine from red meat, fish,…

Creatine kinase (CK) is an enzyme that helps regenerate ATP energy, by moving a phosphate from phosphocreatine to ADP. It is busiest in tissues with high, fluctuating energy…

Creatinine is a waste product from your muscle's creatine. Your body makes it at a fairly steady rate, and your kidneys clear it (mostly by filtration, with a little tubular…

CRISPR-based therapies use CRISPR-Cas9, base editors, or prime editors to make targeted, somatic edits to your DNA. The edits can be done ex vivo (in cells taken out of you) or…

Critical power (CP) is your aerobic 'ceiling'. It is the highest power output (or running speed, called critical velocity) you can sustain without fatiguing out. Just below CP,…

CRON stands for Caloric Restriction with Optimal Nutrition. It is a structured way of eating less. You cut your energy intake by roughly 20 to 30%. At the same time, you…

CSF biomarkers for Alzheimer's are proteins measured in your spinal fluid (via a lumbar puncture) that mirror the core brain pathologies. As amyloid gets locked into plaques,…

Cuproptosis is a form of controlled cell death driven by copper. It is distinct from other death programs like apoptosis, ferroptosis, necroptosis, and pyroptosis. Here is how it…

Curcumin is the main polyphenol in turmeric (Curcuma longa). It tunes several inflammatory and oxidative pathways, including NF-kB and Nrf2. But there is a big practical problem.…

Cycloastragenol is the 'aglycone' (sugar-free core) of astragaloside IV. It is a cycloartane-type triterpenoid, made by breaking down a compound from Astragalus membranaceus…

Cystatin C is a small protein (13 kDa) that inhibits certain enzymes (cysteine proteases). All your nucleated cells make it at a steady rate. Your kidneys' filters (glomeruli)…

HOMA-β (Homeostatic Model Assessment of Beta-cell function) is a quick estimate of how well your pancreas makes insulin. It uses just fasting blood values. The formula is (20 ×…

D-dimer is a scrap left over when your body breaks down a blood clot. An enzyme called plasmin chops up stabilized fibrin, the clot's mesh. D-dimer is the debris. So it acts as a…

Daily step count is the total walking steps you rack up in 24 hours, measured by pedometers or wearables that detect vertical motion. It acts as a device-agnostic proxy for your…

The Disability-Adjusted Life Year (DALY) is the central metric of the Global Burden of Disease framework. It expresses a population's health loss, including the years you might…

DamAge and AdaptAge are 'causality-aware' epigenetic clocks. Kejun Ying and colleagues built them in the Gladyshev lab at Harvard / Brigham and Women's Hospital (Nature Aging,…

D+Q is one of the most-studied senolytic combinations. It pairs dasatinib (a tyrosine-kinase-inhibitor cancer drug) with quercetin (a plant flavonoid). You take it…

De novo lipogenesis (DNL) is how your liver turns excess carbs, mainly glucose and fructose, into new fat. The fat is packaged as triglycerides into VLDL particles, or stored as…

Deep sleep, also called slow-wave sleep (N3), is marked by high-amplitude 'delta' waves on the EEG, and the highest arousal threshold (it is the hardest stage to wake you from).…

The default mode network (DMN) is a set of connected brain regions that switch on when your mind is at rest, and switch off during focused tasks. The core hubs include the medial…

Delayed-onset muscle soreness (DOMS) is the diffuse ache, stiffness, and tenderness that shows up 24 to 72 hours after unfamiliar or eccentric-heavy exercise. It peaks around 48…

Dendritic cells (DCs) are antigen-presenting cells, made in your bone marrow, that bridge innate and adaptive immunity. Two main types circulate in your blood. Plasmacytoid DCs…

Denosumab is a fully human antibody that blocks a signal called RANKL. RANKL is the cytokine that bone-dissolving cells (osteoclasts) need to form, activate, and survive. By…

Detraining is the partial or full reversal of training gains that happens when you cut back or stop exercising. How fast and how much you lose depends on your training history…

A DEXA scan (dual-energy X-ray absorptiometry) measures your body composition and bone density. It passes two X-ray beams at different energy levels through your body and…

DHEA (dehydroepiandrosterone) circulates mainly as DHEA-S. It is a precursor that your peripheral tissues use to make testosterone and estradiol. Serum DHEA-S peaks in early…

Dehydroepiandrosterone sulfate (DHEA-S) is the sulfated, long-lasting form of DHEA. Your adrenal cortex (the zona reticularis) secretes it. It is a precursor that your peripheral…

Dietary fiber is the plant carbohydrate your gut enzymes cannot break down. It comes in two main types. Soluble fiber (like pectin, beta-glucan, and inulin) dissolves in water…

Dietary nitrate (NO₃⁻) is abundant in beetroot, leafy greens, and celery. Your body converts it to nitric oxide (NO) in a two-step cascade. First, your salivary glands…

The disposable soma theory, proposed by Thomas Kirkwood in 1977, says your body has to budget its limited energy. It splits resources between maintaining the body (somatic…

Dim Light Melatonin Onset (DLMO) is a specific time in the evening. It is when your body's own melatonin, in saliva or plasma, rises above a set threshold. The measurement is…

DNA damage is any chemical or structural change to your genome. It includes base modifications, single- and double-strand breaks, and crosslinks. It comes from reactive oxygen…

DNA methylation is one of the main ways your cells control which genes are switched on, without changing the DNA code itself. Enzymes called DNA methyltransferases stick small…

DNA repair pathways are the conserved systems your cells use to find and fix genetic damage. The load is huge. Internal sources alone cause up to 100,000 lesions per cell per…

The DNAm Skin & Blood clock was published by Horvath and colleagues in 2018. It estimates your epigenetic age from 391 CpG sites. Those sites were picked from methylation arrays…

DNAmTL is an epigenetic estimate of your telomere length. It is derived from the methylation levels of 140 CpG sites in blood DNA. It was trained with elastic-net regression,…

DNA methyltransferases (DNMTs) are the enzymes that add methyl tags to your DNA. They move a methyl group from SAM (S-adenosylmethionine) onto a cytosine base, mostly at 'CpG'…

Donanemab is a humanized IgG1 monoclonal antibody. It targets a specific, pyroglutamate-modified end of amyloid-beta (called N3pG). That target appears almost only in established…

DunedinPACE (Pace of Aging Calculated from the Epigenome) is an epigenetic clock published in 2022 by Belsky and colleagues. Unlike most clocks, it estimates your rate of…

Dynapenia is the age-related loss of muscle strength and power, separate from the loss of muscle mass. Clark and Manini coined the term in 2008. They wanted to distinguish…

Dysbiosis is when your gut microbial community drifts away from a healthy state. The drift can be in its makeup, its diversity, or its chemical output. It is a working term, not…

Eccentric training emphasizes the lengthening phase of a muscle contraction. Think of the lowering part of a squat or a curl. Your muscles can produce more force when lengthening…

Echocardiography is a heart ultrasound, done either from the chest (TTE) or down the esophagus (TEE). It is the most widely used cardiac imaging test. It measures your…

Ectopic fat is fat stored in or around organs that normally hold very little of it. Think liver, muscle, pancreas, and heart. It is different from the fat under your skin or…

EGCG (epigallocatechin gallate) is the most abundant catechin in green tea. It is a polyphenol. It has antioxidant, anti-inflammatory, and AMPK-tuning activity. Observational…

Elastin is the matrix protein that lets your tissues stretch and snap back, especially your artery walls, lungs, and skin. Here is the catch: your body lays down almost all of…

The electron transport chain (ETC) is a set of four protein complexes in your inner mitochondrial membrane. They are Complex I (NADH:ubiquinone oxidoreductase), Complex II…

Endocrine-disrupting chemicals (EDCs) are outside substances that mess with your hormones. They block, mimic, or derail how hormones are made, moved, or sensed. Two famous…

Endothelial dysfunction is when the thin inner lining of your blood vessels (the endothelium) stops keeping them healthy. The classic problem: it makes too little usable nitric…

Enterotypes are proposed 'types' of gut microbial community. Think blood types, but for your gut bugs. Arumugam et al. (2011, Nature) first defined them. They used 39 metagenomes…

Epicardial adipose tissue (EAT) is the visceral fat sitting right on your heart, between the heart muscle and its surrounding sac (the pericardium). It is unusual: it shares the…

Your epigenetic age estimates how old your body seems biologically, read from chemical tags on your DNA. Certain spots on the genome (CpG sites) gain or lose methyl groups over…

Epigenetic alterations are age-related changes in how your genes are switched on and off, without any change to the DNA code itself. They include shifts in DNA methylation, in…

Epigenetic drift is the slow, mostly random divergence of DNA methylation patterns over time. It happens between cells, between tissues, and between people, as you age. The…

An epigenome-wide association study (EWAS) is a hypothesis-free scan. It tests whether DNA methylation at hundreds of thousands of CpG sites (spots where a cytosine next to a…

Epitalon (Ala-Glu-Asp-Gly) is a synthetic peptide of four amino acids (a tetrapeptide). Vladimir Khavinson's group developed it in the 1980s and 90s, at the St Petersburg…

EPOC is the extra oxygen your body keeps taking in after exercise ends. Your body uses it to restore ATP and creatine phosphate, clear lactate, refill oxygen stores, and bring…

ER stress happens when your cells' protein-folding factory gets overwhelmed. The endoplasmic reticulum (ER) folds, modifies, and quality-checks proteins headed for secretion or…

Ergothioneine is a sulfur-containing compound (a histidine betaine), mostly in its 'thione' form. Only fungi, certain bacteria, and cyanobacteria can make it. You get it from…

Estradiol (E2) is the most biologically active estrogen. Before menopause, it is made mainly in the ovaries. Smaller amounts come from converting androgens, a process called…

Exosomes are tiny membrane vesicles (30 to 150 nm across) that cells release from an internal sorting system. They carry a cargo of proteins, lipids, mRNAs, microRNAs, and other…

Your exposome is the sum of every environmental exposure you meet from conception to death: chemical, physical, biological, lifestyle, and social. Christopher Wild coined the…

The extracellular matrix (ECM) is the protein-and-sugar scaffold that holds your tissues together. It also passes chemical and mechanical signals to the cells living in it. As…

Extracellular vesicles (EVs) are tiny membrane bubbles that nearly every cell releases. They come in rough size classes: exosomes (30 to 150 nm, born inside the cell),…

F2-isoprostanes are markers of oxidative stress in your body. They form when free radicals attack a fat (arachidonic acid) in your cell membranes, creating compounds that look…

Faecal microbiota transplant (FMT) moves processed stool from a healthy donor into a recipient's gut. The goal is to rebuild a disrupted microbial community. It has exactly one…

Faecalibacterium prausnitzii is a strict-anaerobe Firmicute, and one of the most abundant butyrate-making bacteria in a healthy adult colon. It often makes up several percent of…

Fasting glucose is your blood-sugar level after at least eight hours without eating. It reflects your baseline glucose balance. Several things set that balance. They are your…

Fasting insulin measures the insulin in your blood after an overnight fast. It reflects three things at once. First, your β-cells' output. Second, how much insulin your liver…

The fasting-mimicking diet (FMD) is a 5-day plan that is low in calories, low in protein, and plant-based. Valter Longo's group designed it. It copies the metabolic effects of a…

Ferritin is the protein your cells use to store iron, and a little of it leaks into your blood. That is why serum ferritin is the go-to blood test for your total iron stores. Low…

Ferroptosis is a controlled form of cell death driven by iron and runaway fat oxidation. Iron lets lipid peroxides (oxidized fats) build to lethal levels, which sets it apart…

FGF21 (fibroblast growth factor 21) is a hormone, mostly made by your liver. It is released in response to fasting, low protein intake, and mitochondrial stress. It acts on…

Fibrinogen (also called clotting factor I) is a large protein your liver makes that turns into fibrin, the mesh that forms a blood clot. It is also an 'acute-phase reactant',…

FibroScan (vibration-controlled transient elastography, VCTE) measures how stiff your liver is, in kilopascals (kPa). It sends a low-frequency shear wave through the liver and…

Fibrosis is scarring gone overboard. When a tissue is injured, inflamed, or full of senescent cells, specialized cells called myofibroblasts lay down too much connective tissue…

Fisetin is a flavonoid (a plant compound) found in strawberries, apples, and persimmons. So you already eat a little. In aged mice, one study (Yousefzadeh et al., 2018,…

Flavonoids are a big subclass of plant polyphenols, built on a 15-carbon backbone. They come in six families. Flavonols (quercetin, kaempferol; onions, kale). Flavan-3-ols…

Flow, described by psychologist Mihaly Csikszentmihalyi, is a state of deep absorption in a challenging task that is well matched to your skill. In flow, your self-awareness…

Flow-mediated dilation (FMD) is a non-invasive ultrasound test of how well your blood-vessel lining (the endothelium) works. It measures the percentage that your brachial (arm)…

Fluid versus crystallized intelligence is a split within the Cattell-Horn-Carroll (CHC) framework. It separates two broad mental abilities that age very differently. Fluid…

FOXO proteins (short for Forkhead box O) are key switches in your insulin/IGF-1 pathway. When insulin and IGF-1 signals run low, FOXO enters the nucleus. There it turns on…

FOXO3 is a gene for a transcription factor. It sits at a crossroads of longevity pathways. It integrates signals from the insulin/IGF-1 and AMPK pathways. With those, it controls…

Frailty is a state of heightened vulnerability to stressors. It comes from deficits piling up across many body systems, which drains your reserve and resilience. Two main ways to…

Free fatty acids (NEFA, or non-esterified fatty acids) are long-chain fats floating in your blood. They ride on the protein albumin. They are released when an enzyme…

The free radical theory of aging was proposed by Denham Harman in 1956. It originally blamed aging on one thing. That is the cumulative damage to your cells from oxygen-derived…

Free radicals are atoms or molecules with one or more unpaired electrons. That makes them highly reactive. They come from your normal metabolism, your immune activity, and…

Free T3 (fT3) and free T4 (fT4) are the unbound, active fractions of two thyroid hormones, triiodothyronine and thyroxine. T4 is the main hormone your thyroid secretes. Your…

Free testosterone is the small slice of your testosterone that floats free in your blood. Most of it is bound to two proteins, SHBG and albumin. Only the 1 to 4% that is unbound…

Fructosamine means your glycated serum proteins, chiefly albumin, formed when glucose sticks on non-enzymatically and rearranges into a stable ketoamine (the Amadori product).…

Gait speed, usually measured over a 4- or 6-meter walk at a comfortable pace, is one of the strongest and cheapest functional markers of whole-body aging. A single number rolls…

Galectin-3 is a small protein (a lectin) released by your activated immune cells (macrophages). It pushes heart fibroblasts to multiply, lay down collagen, and remodel the heart…

GDF11 (growth differentiation factor 11) is a signaling protein in the TGF-β family. In the embryo, it has a well-established job: helping pattern the body axis and organs, by…

GDF15 (growth differentiation factor 15), also called MIC-1, is an unusual member of the TGF-β protein family. Normally it sits at low levels. But it shoots up under…

Gene therapy delivers genetic material to add, silence, or edit your genes. It usually uses AAV viral vectors for stable, long-term gene expression. Or it uses lipid…

Genomic instability is the slow build-up of damage to your DNA, both in the nucleus and in the mitochondria. It includes point mutations, reshuffled chromosomes, copy-number…

Gerontology is the scientific study of aging. It covers the biology, the psychology, and the social side of getting older. It became a formal field in the early 20th century.…

A geroprotector is any drug, supplement, or lifestyle change that targets the basic mechanisms of aging. The goal is to extend your healthspan. Unlike treatments aimed at one…

Geroscience is an interdisciplinary field that studies the biological mechanisms of aging, and how they causally drive chronic disease. Researchers at the Buck Institute coined…

GFAP (glial fibrillary acidic protein) is the main structural fiber inside mature astrocytes. (Astrocytes are a type of brain support cell.) It is a marker of 'reactive…

GGT (gamma-glutamyl transferase) is an enzyme anchored in cell membranes that helps recycle glutathione, your body's master antioxidant. It is most active in your liver, bile…

GHK-Cu is the tripeptide glycyl-L-histidyl-L-lysine, bound to copper(II). It is a fragment of a larger blood protein (α2-macroglobulin), whose level in your plasma drops with…

GLP-1 receptor agonists copy a gut hormone called glucagon-like peptide-1. Examples are liraglutide, semaglutide, and dulaglutide. They prompt your pancreas to release insulin…

Glucagon is a hormone (29 amino acids long) made by your pancreas's alpha-cells. It is released when your blood sugar drops, during long fasts, and after you eat protein, and it…

Gluconeogenesis is how your liver (and, in long fasts, your kidney) makes new glucose from non-carb sources. The main precursors are lactate, glycerol, and 'glucogenic' amino…

Glucosamine is an amino sugar your body makes itself. It is a building block of glycosaminoglycans, the long sugars that keep cartilage hydrated, springy, and able to take…

Glucose variability is how much your blood sugar swings up and down over hours and days. It is measured a few ways. Common ones are the standard deviation, the coefficient of…

Glutathione (GSH) is your cells' main built-in antioxidant. It is a small molecule (a thiol) that your body makes in two energy-using steps from three amino acids: glutamate,…

GlycA is a blood marker of long-term, low-grade inflammation. It is read by NMR (nuclear magnetic resonance) spectroscopy. The signal comes from sugar groups (N-acetyl methyl…

GlycanAge is a biological-age test based on the sugar coating of your antibodies. Your antibodies (immunoglobulin G, or IgG) carry small branched sugar chains called N-glycans.…

Glycation is the non-enzymatic sticking of sugars, like glucose or fructose, onto your proteins, fats, or DNA. Through the Maillard reaction, it first makes unstable Schiff…

The glycemic index (GI) ranks foods by how fast their digestible carbs raise your blood sugar, compared with pure glucose (GI = 100). A GI of 55 or under is low, 56 to 69 is…

Glycine is the smallest, simplest amino acid. It is 'non-essential' under normal conditions. But it is 'conditionally essential' in aging, pregnancy, and disease. In those…

The glymphatic system, described by Iliff, Nedergaard, and colleagues in 2012, is your brain's waste-clearance pathway. Cerebrospinal fluid flows along the spaces around blood…

GlyNAC is the combined supplement of glycine plus N-acetylcysteine (NAC). The aim is to refill both building blocks of glutathione (the tripeptide γ-Glu-Cys-Gly), which falls…

Gompertz law, set out by the British actuary Benjamin Gompertz in 1825, captures a striking pattern: in adults, your risk of dying rises exponentially with age. To be exact, the…

Green space exposure means how close you live to, or how much time you spend in, vegetated places: city parks, street trees, or forests. It includes the Japanese practice of…

GrimAge is a second-generation epigenetic clock. Lu et al. introduced it in 2019, with Steve Horvath as senior author. Instead of predicting your chronological age, it is trained…

Grip strength is the maximal force you generate when you squeeze a device called a dynamometer. It is a cheap, simple proxy for your whole-body muscular function. In the…

Growth hormone (GH, somatropin) is a peptide hormone from your anterior pituitary. It shapes body composition, bone density, and metabolism, mostly by making your liver produce…

Your gut microbiota is the community of roughly 38 trillion bacteria (plus archaea, fungi, and viruses) living in your gut, densest in the colon. Together they carry a gene…

The gut-brain axis is the two-way communication line between your gut and your brain. It runs over several channels: the gut's own nervous system, the vagus nerve, the…

A genome-wide association study (GWAS) is a hypothesis-free scan of the common variants in your DNA (SNPs, usually present in over 1 to 5% of people) across the whole genome. It…

HALE (Healthy Life Expectancy) is a WHO summary measure. It is the average number of years you can expect to live in full health. To get it, you take total life expectancy and…

The Hallmarks of Aging are a checklist of the main things that go wrong in your body as you age. Biologists Lopez-Otin and colleagues came up with the framework. The 2023 update…

The Hannum clock is a blood-based epigenetic age estimator, published by Gregory Hannum and colleagues in 2013. It uses DNA-methylation levels at 71 CpG sites, taken from…

The Hayflick limit is the most times a normal human body cell can divide in culture, typically 40 to 60 times, before it stops and enters replicative senescence. Leonard Hayflick…

A hazard ratio (HR) tells you how fast events happen in one group versus a reference group, at any given moment during follow-up. Formally, it is the ratio of the instant event…

HbA1c (glycated hemoglobin) is the share of your hemoglobin that is stably bound to glucose. It gives an integrated picture of your average blood glucose over roughly the past 2…

HDL (high-density lipoprotein) is the 'good' cholesterol carrier. It picks up cholesterol from your tissues and brings it back to your liver. That return trip is called 'reverse…

Healthspan is the period of your life spent in good health, free from serious chronic disease and major functional impairment. It is conceptually distinct from lifespan, which…

Heart rate recovery (HRR) is how fast your heart rate drops after you stop hard exercise. It is measured in the first minute (HRR1) or the first two minutes (HRR2) after a peak…

Heart rate variability (HRV) is the tiny beat-to-beat change in the time between your heartbeats, measured in milliseconds. Within a healthy sinus rhythm, higher values usually…

Heat shock proteins (HSPs) are a family of highly conserved 'molecular chaperones'. They are named for being induced by heat, but they are active under many kinds of stress. They…

The heat shock response is a conserved cellular program. It is triggered by high temperature and other 'proteotoxic' stresses (things that damage proteins). A master switch, heat…

Lead, cadmium, and inorganic mercury are the heavy metals most consistently linked to chronic low-level exposure and harm in human studies. Each has its own route in. Lead comes…

Hematopoietic stem cells (HSCs) are the rare master cells in your bone marrow that make blood for your whole life. They do it by dividing in a way that both renews themselves and…

Hepatic insulin resistance means your liver stops listening to insulin's 'stop making sugar' signal after meals, even though it still obeys insulin's 'make fat' signal.…

Heritability of lifespan is the share of the variation in age-at-death that comes from inherited genetic differences in a given population. Classic twin studies put it at roughly…

Heterochromatin is the tightly packed, switched-off part of your DNA. It is held shut by chemical marks on the histone proteins (like H3K9me2/3 and H3K27me3). Helpers such as HP1…

Heterochronic parabiosis (HCP) is an experiment where a young and an old animal are surgically joined so they share one blood supply. Each is continuously exposed to the other's…

Frequency-domain HRV analysis breaks your heartbeat-interval signal into frequency bands. The high-frequency band (HF, 0.15 to 0.4 Hz) mostly reflects your vagus nerve's…

HIF-1α is the part of a master switch your cells use to respond to low oxygen. It is the oxygen-sensitive half of a transcription factor called HIF-1 (one half, HIF-1α, plus a…

High-sensitivity troponin (hs-Tn) is a blood test for heart-muscle injury. It measures the cardiac proteins troponin I (hs-TnI) or troponin T (hs-TnT) in your blood, at levels…

HIIT (high-intensity interval training) alternates short bursts of near-maximal effort with periods of easy recovery. A session usually runs 10 to 30 minutes total. The hard…

The Hippo pathway is an ancient kinase cascade that controls organ size, tissue balance, and stem-cell activity. Its core kinases (MST1/2 and LATS1/2) work by tagging two…

Hippocampal volume measures the size of the hippocampus. That is the brain region central to memory consolidation and spatial navigation. Atrophy rates vary by cohort and method.…

Histone modifications are reversible chemical changes to histone proteins. (Your DNA wraps around those proteins.) They include acetylation, methylation, phosphorylation, and…

HOMA-IR (Homeostatic Model Assessment of Insulin Resistance) is a fasting blood index of insulin resistance. You calculate it as (fasting insulin in µU/mL × fasting glucose in…

Homocysteine is a sulfur-containing amino acid your body makes while processing methionine. It is cleared in two ways: remethylation or transsulfuration. Both depend on folate,…

Hormesis is the idea that a little bit of a stressor can be good for you, even though a lot of it would hurt you (scientists call this a biphasic dose-response). The dose makes…

Menopausal HRT replaces estrogen, usually combined with a progestogen if you have a uterus. It relieves hot flushes and other vasomotor symptoms, protects your bones, and treats…

The Horvath clock is a multi-tissue epigenetic age estimator, published by Steve Horvath in 2013. It uses DNA-methylation levels at 353 CpG sites to predict your chronological…

hs-CRP (high-sensitivity C-reactive protein) is a blood marker of inflammation. Your liver makes CRP, mainly when prompted by the signal IL-6. The 'high-sensitivity' assay can…

Humanin is a 24-amino-acid peptide. It is encoded inside your mitochondrial DNA, in the 16S rRNA region. Hashimoto and Nishimoto first found it in surviving neurons of…

Hydroxytyrosol is the main antioxidant phenol in olive oil and olive leaves. (It is an ortho-diphenolic compound.) In the fruit and the oil, it sits mostly bound inside a bigger…

Hyperbaric oxygen therapy (HBOT) delivers 100% oxygen at high pressure. The pressure is typically 2.0 to 2.4 times normal atmospheric pressure (the clinical threshold for HBOT is…

The hyperfunction theory of aging was proposed by Mikhail Blagosklonny in 2006. It offers a different cause of aging. It says aging is driven by growth pathways that stay…

Hypoxia training deliberately exposes your body to less oxygen. It can be steady (altitude, hypoxic tents) or in on-off cycles (intermittent hypoxia). The reported payoff: it…

iAge is an 'inflammatory age' score, introduced by Sayed and colleagues (2021, Stanford). It uses a deep-learning model, trained on a panel of 50 blood cytokines and chemokines,…

Insulin-like growth factor 1 (IGF-1) is made mainly in your liver, under stimulation from growth hormone (GH). It carries out many of GH's anabolic effects on muscle, bone, and…

IGF-1 signaling is the cascade that fires when insulin-like growth factor 1 binds its receptor in your cells. It switches on two parallel branches, PI3K/AKT and MAPK/ERK.…

Ikigai is a Japanese concept, loosely translated as a sense of purpose or a reason for being. It covers everyday sources of meaning, like your relationships, your routines, and…

Interleukin-10 (IL-10) is your immune system's main 'calm down' signal. It is an anti-inflammatory cytokine, made mostly by macrophages, regulatory T cells, and B cells. It tamps…

IL-1β (interleukin-1 beta) is a powerful pro-inflammatory cytokine. Your monocytes and macrophages make it. It drives acute inflammation. It also drives 'inflammaging', the…

Interleukin-6 (IL-6) is a versatile cytokine. It is made by immune cells, fat cells, blood-vessel cells, and senescent cells. It signals two ways: through a membrane-bound…

Immunosenescence is the age-related rewiring of your immune system. Three things drift. Your thymus and bone marrow make fewer fresh (naive) lymphocytes. Older, experienced…

The incretin effect is a striking observation: drinking glucose triggers a bigger insulin response than getting the same amount of glucose by IV. The difference comes from gut…

Indole-3-propionic acid (IPA) is a compound your gut microbes make from dietary tryptophan. Almost only one strict anaerobe, Clostridium sporogenes, produces it, by converting…

Indoor air quality (IAQ) is the chemical, biological, and physical makeup of the air inside buildings. Adults in rich countries spend about 90% of their time indoors. The key…

Inflammaging is the chronic, low-grade, sterile inflammation that builds up as you age. It happens even without any infection. It shows up as raised baseline levels of…

Insomnia is a sleep disorder: persistent trouble falling asleep, staying asleep, or getting restful sleep, despite having enough time to sleep, and it causes real daytime…

Insulin resistance is when your tissues stop responding well to insulin, so your pancreas has to pump out more to keep blood sugar in check. It is driven by belly fat (visceral…

Insulin sensitivity is how well your cells respond to insulin. The key cells are in muscle, liver, and fat. When insulin works, they take up glucose, and the liver shuts off its…

The insulin/IGF-1 pathway (often shortened to IIS) is one of your body's main nutrient sensors. When insulin and IGF-1 (a growth hormone) latch onto their receptors, they switch…

The integrated stress response (ISR) is a built-in alarm system your cells use to cope with trouble. No matter the threat, it funnels down to one move: switching off a key…

Intermittent fasting is an umbrella term for eating patterns that alternate normal eating with longer fasting windows. Common forms include 16:8 time-restricted eating,…

Intestinal permeability is the regulated passage of molecules between the cells lining your gut. It is controlled by 'tight junction' complexes (claudins, occludin, ZO-1, and…

Ionized calcium (iCa²⁺), also called free calcium, is the active part of your blood calcium. It makes up about 45 to 50% of the total. The rest is bound to albumin or tied up…

Induced pluripotent stem cells (iPSCs) are adult body cells reprogrammed back into a flexible, pluripotent state. Researchers do it with factors called OSKM (Oct4, Sox2, Klf4,…

Ischemic preconditioning (IPC) is a hormetic trick. Brief, non-lethal cycles of cutting off a tissue's oxygen, then restoring it, protect that tissue against a later, lethal loss…

Isometric training means contracting a muscle against an immovable resistance, with no joint movement. Think planks, wall sits, or holding a mid-range squat. It builds tendon…

The JAK-STAT pathway is a fast signaling relay from your cell surface to its nucleus. (JAK = Janus kinase; STAT = signal transducer and activator of transcription.) Many…

The Kaplan-Meier estimator is a nonparametric way to estimate the survival function, S(t). That is the probability of surviving beyond a given time, t, from time-to-event data…

The ketogenic diet is a very-low-carb (usually under 50 g a day), high-fat, moderate-protein way of eating that keeps your body in steady ketosis (burning fat for fuel and making…

Ketone bodies are your body's backup fuel for when carbs run low. There are three of them. They are beta-hydroxybutyrate, acetoacetate, and acetone. Your liver makes them inside…

Ketosis is a fuel-switch in your body. When glucose runs low, your liver turns fat into ketone bodies. There are three: beta-hydroxybutyrate (BHB), acetoacetate, and acetone.…

The Klemera-Doubal method (KDM) is a statistical algorithm that estimates your biological age from clinical biomarkers. It works by minimizing the squared distances between a set…

Klotho (here meaning alpha-Klotho, distinct from beta-Klotho) is a membrane-spanning protein, made mostly in your kidney and brain. After it is cleaved, it also circulates as a…

Klotho is a protein that drops sharply as you age. It acts as a co-receptor for the hormone FGF23. Its soluble, circulating form (s-Klotho) dampens Wnt and TGF-β signaling. In…

The KL-VS haplotype of the klotho gene is a set of six linked variants. Two of them change amino acids (F352V and C370S) in exon 2. It raises serum klotho protein. And it is tied…

Alpha-ketoglutarate (AKG) is a key intermediate in the TCA (citric acid) cycle. It also acts as a required co-substrate for a large family of enzymes (dioxygenases). Those…

Lactate threshold is used loosely for two points. LT1 (the aerobic threshold, around 2 mmol/L) is where your blood lactate first rises above baseline. LT2 is the highest…

Lactobacillus is a group of Gram-positive bacteria. They make lactic acid. You meet them in fermented foods and probiotics. In 2020, Zheng and colleagues reorganized the genus.…

Lamin A is a structural protein (an intermediate filament) and a major part of the nuclear lamina, the mesh just under your cell's inner nuclear membrane. It is essential for…

The mortality plateau (late-life mortality deceleration) is a striking observation. Past about age 105, your risk of dying stops climbing exponentially. Instead it flattens to a…

LC3 lipidation is a key step in building an autophagosome (the autophagy 'garbage bag'). It attaches the autophagy protein LC3 to a membrane fat (phosphatidylethanolamine, or…

LDL (low-density lipoprotein) is the cholesterol carrier that drives heart disease. When you have too many ApoB-carrying LDL particles, they slip into your artery wall (the…

LDL-P (LDL particle number) counts how many LDL particles are in your blood, rather than how much cholesterol they carry. It is usually measured by NMR spectroscopy or…

Lecanemab is a humanized antibody. It binds soluble amyloid-beta 'protofibrils' (and, less so, fibrous plaques). In the phase 3 CLARITY-AD trial, it slowed decline on a standard…

Leptin is a hormone your white fat releases, in proportion to how much fat you carry. It acts on receptors in your hypothalamus (especially the arcuate nucleus) to curb appetite…

Leukocyte telomere length (LTL) is the average length of the repetitive TTAGGG caps on your chromosome ends, in your white blood cells. It is measured in kilobases (kb) and used…

Lewy bodies are clumps that build up inside your brain cells, made mostly of a misfolded protein called α-synuclein. Friedrich Lewy first described them in 1912, and they are the…

Lifespan is the total length of time an organism lives, from birth to death, usually expressed in years for humans. At the population level, it is summarized by life expectancy,…

Artificial light at night (ALAN), from streetlights, screens, and indoor bulbs, throws off your body clock. It works through special cells in your retina (ipRGCs, which carry a…

LINE-1 (long interspersed nuclear element-1, or L1) is a type of 'jumping gene' (a retrotransposon) that makes up roughly 17% of your genome. It encodes two proteins (ORF1p and…

Lipid peroxidation is a chain-reaction form of fat damage. It hits the polyunsaturated fats (PUFAs) in your cell membranes, lipoproteins, and fat droplets. It kicks off when a…

Lipofuscin is the 'age pigment', a yellow-brown gunk that builds up inside your cells. It is made of cross-linked, oxidized proteins, damaged fats, sugar add-ons, and reactive…

Trace lithium comes from drinking water (about 0.01 to 0.1 mg/L). In ecological studies in Japan, Texas, and Europe, more of it has been linked to lower all-cause death. The…

MRI-PDFF (proton density fat fraction) measures the share of your liver's protons that belong to fat triglycerides, versus all its water and fat protons. The result is a…

LMNA is a gene that makes two nuclear-skeleton proteins, Lamin A and Lamin C (via alternative splicing). These lamins form a mesh just under the inner nuclear membrane of your…

Loneliness is the subjective feeling of being socially disconnected. It is now a recognized risk factor for heart disease, dementia, and early death. Meta-analyses by…

Longevity escape velocity is the idea of a tipping point where medicine adds more than a year to your remaining life expectancy for every year that passes, so you would…

Loss of proteostasis is one of the established hallmarks of aging. The word 'proteostasis' means protein balance. This hallmark is the age-related decline of your protein…

Annual low-dose chest CT (LDCT) screens current and former heavy smokers for early-stage lung cancer, at an effective dose of roughly 1 to 2 mSv. The landmark US National Lung…

Lp-PLA2 is an enzyme tied to vascular inflammation. (Its other name is platelet-activating factor acetylhydrolase.) It is made mainly by macrophages and lymphocytes, and in your…

Lipoprotein(a), or Lp(a), is an LDL-like particle. In it, apolipoprotein(a) is covalently linked to apoB-100 through a disulfide bond. Your plasma level is largely genetic (often…

Lipopolysaccharide (LPS) is a building block of the outer wall of Gram-negative bacteria. When bacteria die or divide and shed it, LPS is the single most potent trigger for an…

Lutein and zeaxanthin are two xanthophyll carotenoids (dihydroxy types). They build up in your macula, the central retina, where they form the 'macular pigment' and filter blue…

Lycopene is an acyclic, fat-loving carotenoid (a plant pigment) that gives tomatoes, watermelon, and pink grapefruit their red color. You absorb it better from heat-processed…

The absolute lymphocyte count (ALC) is the total number of lymphocytes circulating in your blood. That includes your T cells, B cells, and NK cells. It comes from the…

The lysosome is a membrane-bound compartment inside your cells. It is filled with acidic digestive enzymes (hydrolases). It breaks down proteins, fats, nucleic acids, and…

The M1/M2 framework describes two opposite 'modes' your macrophages can switch into. (Macrophages are immune cleanup cells.) M1 macrophages, called classically activated, are…

Serum magnesium measures only the small slice of your body's magnesium that is in your blood. About 99% is locked away in bone, muscle, and soft tissue. So a blood test is a poor…

Mammography is a low-dose X-ray image of the breast (an effective dose of roughly 0.4 mSv per two-view, both-sides study). It is the only method with randomized-trial evidence…

MASLD (metabolic dysfunction-associated steatotic liver disease) is the 2023 rename of what used to be called non-alcoholic fatty liver disease (NAFLD). Major liver societies…

Maximum heart rate (HRmax) is the highest beats per minute your heart reaches during all-out effort. It is mostly set by your age and genetics, not your fitness, and it declines…

Maximum lifespan is the oldest age a member of a species can reach under ideal conditions. It is the documented or theoretical ceiling, not the population's average life…

Multi-cancer early detection (MCED) tests are blood tests. They scan the cell-free DNA floating in your plasma. They look mainly at two things: methylation patterns and the…

The Mediterranean diet is an eating pattern built around vegetables, fruits, legumes, whole grains, nuts, olive oil, and fish, the kind of meals you can eat every day, with…

Melatonin is a hormone secreted by your pineal gland in response to darkness. It signals biological night and helps align your circadian system. It helps you fall asleep,…

Mendelian randomization (MR) is a clever way to test cause without a trial. It uses inherited genetic variants (usually SNPs tied to an exposure in a GWAS) as natural stand-ins…

Mesenchymal stem cells (MSCs) are versatile stromal cells. They can turn into bone, cartilage, and fat cells. They are harvested from bone marrow, fat, umbilical cord (Wharton's…

A meta-analysis is a statistical method that quantitatively combines results from multiple independent studies on the same question. It yields a pooled effect estimate, with…

The metabolic equivalent of task (MET) is a unit for the energy cost of an activity. It expresses that cost as a multiple of your resting metabolic rate. By definition, 1 MET is…

Metabolic flexibility is your body's ability to switch fuel sources smoothly. The two main fuels are glucose and fatty acids. You switch between them as you eat, fast, and move.…

Metabolic syndrome is a cluster of linked cardiometabolic risk factors that sharply raise your risk of type 2 diabetes, heart disease, and early death. The most-used criteria…

Metformin is a cheap, decades-old diabetes pill (a biguanide). Doctors reach for it first in type 2 diabetes. It does two main things. It tells your liver to make less new sugar…

Methionine restriction (MR) means cutting the sulphur amino acid methionine in your diet, without an overall cut in calories. Orentreich and colleagues first reported, in 1993,…

Methylene blue (MB) is a synthetic dye (a phenothiazine), FDA-approved (as Provayblue, 2016) to treat a blood disorder called acquired methemoglobinemia. The starting dose there…

Methylglyoxal (MGO) is a highly reactive, damaging molecule (a dicarbonyl) that your cells make as an accidental byproduct of glycolysis (sugar-burning). It is the main…

Microbial beta-glucuronidases (GUS) are enzymes made by many of your gut bacteria. (They live in the Firmicutes, Bacteroidota, and Enterobacteriaceae.) They snip off glucuronide…

Microbiome diversity measures how rich and even your gut community is. 'Alpha diversity' is within one sample. 'Beta diversity' is across samples. The Shannon index is a popular…

Microglia are your brain's resident immune cells. They come from yolk-sac precursors that colonize the brain early in embryo development, and they renew themselves without help…

Microplastics are solid plastic particles smaller than 5 mm (including nanoplastics, which are sub-micron). They come from larger plastic debris breaking down, plus synthetic…

Mild cognitive impairment (MCI) sits between normal aging and dementia. By Petersen's criteria, it means tests show a real cognitive decline, but you still handle daily life on…

The MIND diet (Mediterranean-DASH Intervention for Neurodegenerative Delay) is a hybrid eating pattern aimed at protecting your brain. It emphasizes leafy greens, berries, nuts,…

Mindfulness is a trained practice. You bring open, non-judgmental attention to the present moment, usually through meditation. Randomized trials show modest but consistent…

Mitochondrial biogenesis is how your cells build more mitochondria, the tiny power plants that make your energy. To pull it off, the cell has to coordinate genes from two places…

Mitochondrial density is how many mitochondria you have per unit of muscle. It also covers how much space they take up. Higher density means more capacity to burn fuel with…

Mitochondrial DNA (mtDNA) is the small, circular genome inside your mitochondria. It is about 16,569 base pairs, present in many copies per cell. It encodes 13 essential parts of…

Mitochondrial dynamics is the constant cycle of fission (splitting) and fusion (merging) that reshapes your mitochondrial network as metabolic needs and stress change. Fission is…

Mitochondrial dysfunction means your cells' power plants are running poorly. (Mitochondria are those power plants.) It shows up in several ways. The cells make less ATP energy.…

Mitochondrial haplogroups are family branches of your mitochondrial DNA (mtDNA), which you inherit only from your mother. Each branch is defined by a shared set of DNA tweaks,…

Mitochondrial respiratory capacity is the top speed at which your mitochondria can push oxygen through their electron transport chain (ETC) to make energy, when fuel and ADP are…

Mitochondrial transplantation means physically moving healthy, working mitochondria (the cell's power plants) into cells or organs whose own mitochondria are failing, for example…

The mitochondrial unfolded protein response (mtUPR) is a stress-signaling pathway inside your mitochondria. It fires when misfolded or clumped proteins overwhelm the…

Mitohormesis is the idea that a little stress from your mitochondria can make you healthier. The stress here is a brief, mild burst of reactive oxygen species (ROS), like…

Mitophagy is your cells' way of recycling broken mitochondria. It is a selective form of autophagy. It targets damaged or 'depolarized' mitochondria. It then ships them to the…

The Mini-Mental State Examination (MMSE), introduced by Folstein, Folstein, and McHugh in 1975, is a 30-point cognitive screening test. It checks orientation, registration,…

The Montreal Cognitive Assessment (MoCA), developed by Ziad Nasreddine and published in 2005, is a 30-point, 10-minute bedside screening test. It covers visuospatial/executive…

Indoor mold grows wherever your building stays damp. The usual culprits are Stachybotrys chartarum, plus Aspergillus and Penicillium species. They can release living spores,…

Mortality doubling time (MDT) is how many years it takes for your age-specific risk of dying to double. It comes straight from the Gompertz exponent b: MDT = ln(2)/b. In today's…

MOTS-c is a 16-amino-acid peptide. It is encoded inside your mitochondrial 12S rRNA region. In rodent studies, it activates AMPK and inhibits the folate-purine cycle. It also…

Myeloperoxidase (MPO) is an enzyme stored in granules of your neutrophils and monocytes. During inflammation, it makes hypochlorous acid (essentially bleach) and other reactive…

MR spectroscopy (MRS) measures the chemistry of your tissues non-invasively, on a standard MRI scanner. It reads the slight frequency shifts in the MR signal to quantify specific…

mtDNA heteroplasmy is when a single cell, tissue, or person carries two or more different mitochondrial DNA sequences. It is a mix of normal (wild-type) and mutant copies. The…

The MTHFR C677T variant (rs1801133) is a common tweak in the MTHFR gene that makes a heat-sensitive, slower version of the enzyme. People with two copies (TT) keep only about 30%…

mTOR is a master growth switch inside your cells. The name stands for "mechanistic target of rapamycin," and it is an enzyme (a serine/threonine kinase) that reads the signals…

mTOR is a master growth-control kinase, and it works inside two distinct teams. mTORC1 is built around a scaffold protein called Raptor. mTORC2 is built around a different one,…

Multimorbidity means having two or more chronic conditions at once, with no single one picked as the main disease, say if you have diabetes, arthritis, and heart disease…

Muscle protein synthesis (MPS) is how your muscle cells build new proteins from amino acids. It drives muscle maintenance, repair, and growth. It is controlled by mTORC1, a…

Mutation accumulation theory is an evolutionary explanation for why you age. Peter Medawar first proposed it in his 1952 lecture, 'An Unsolved Problem of Biology.' The core idea:…

Myostatin, also called GDF8, is a secreted protein in the TGF-β family, and the main brake on your muscle growth. McPherron, Lawler, and Lee first characterized it in 1997. Your…

N-acetylcysteine (NAC) is a tweaked form of the amino acid cysteine. In the clinic, it loosens mucus and serves as the standard antidote for acetaminophen (paracetamol) overdose.…

NAD+ is a helper molecule (a coenzyme) your cells cannot make energy without. It carries electrons during metabolism. It is also the fuel for three groups of enzymes: sirtuins,…

NADH is the reduced form of NAD+. Your cells make it when NAD+ accepts electrons, during glycolysis, the citric acid cycle, and fatty-acid oxidation. NADH then delivers those…

Your T cells come in two broad camps: naive and memory. Naive T cells have not met their target yet. They constantly circulate through your lymph organs, waiting for their…

NAMPT (nicotinamide phosphoribosyltransferase) is the rate-limiting enzyme of the NAD+ 'salvage pathway'. That is the main route your cells use to remake NAD+ from nicotinamide…

Navitoclax (ABT-263) is an orally available 'BH3 mimetic'. It inhibits three anti-death proteins: BCL-2, BCL-xL, and BCL-W. It does this by slotting into their BH3 groove, which…

NEAT (non-exercise activity thermogenesis) is the energy you burn through all your daily movement outside of formal exercise. That means walking, standing, fidgeting, household…

Necroptosis is a controlled but messy way for your cells to die. Unlike tidy apoptosis, the cell bursts open, but it still follows a defined molecular script. The key players are…

Negligible senescence describes organisms that show no measurable decline with age. They do not lose function, they do not face a rising risk of death, and they do not lose the…

Neuroinflammation is when your brain's innate immune system, mainly microglia and astrocytes, gets activated, by protein clumps, injury, or the sterile signals of aging. It…

Neuroplasticity is your brain's lifelong ability to rewire itself, both its structure and its synaptic connections, in response to learning, experience, and injury. It is what…

The neutrophil-lymphocyte ratio (NLR) comes straight from a standard blood count. It is your neutrophil count divided by your lymphocyte count. A typical healthy range is about…

NF-κB is a family of 'master switch' transcription factors for inflammation. (Its full name is nuclear factor kappa-light-chain-enhancer of activated B cells.) The family has…

Neurofilament light chain (NfL) is a structural protein from inside large, myelinated nerve fibers. When nerve axons are injured, NfL leaks into the spinal fluid and blood.…

Nicotinamide (NAM, also called niacinamide) is the amide form of vitamin B3. It is a direct building block for NAD+, via a salvage-pathway enzyme called NAMPT. It is…

Nitric oxide (NO) is a gas that acts as a signaling molecule. Your blood-vessel lining (endothelium) makes it with an enzyme called eNOS (NOS3), converting L-arginine and oxygen…

Natural Killer (NK) cells are part of your innate immune system. They destroy virus-infected and cancerous cells without needing prior 'training' on an antigen. Their action is…

The NLRP3 inflammasome is a multi-protein alarm complex in your cells. It is built from three parts: a sensor (NLRP3), an adaptor (ASC), and pro-caspase-1. It assembles in…

NMN is a building block your body uses to make NAD+, a coenzyme that is central to energy, sirtuin activity, and DNA repair. It enters NAD+ production through the salvage…

Environmental noise pollution is unwanted sound from roads, rail, aircraft, and industry. Chronic exposure raises your heart-disease risk and death, through non-hearing pathways.…

You have probably heard that sugar can stiffen collagen (those are AGE crosslinks). But there is a second, completely different kind your body makes on purpose. An enzyme called…

Non-HDL cholesterol (non-HDL-C) is simply your total cholesterol minus your HDL. It captures the cholesterol in all the 'bad', artery-clogging lipoproteins: LDL, VLDL, IDL,…

Notch signaling is a cell-to-cell communication system that decides cell fates and keeps tissues balanced. It works only by direct contact between touching cells. Here is the…

NR is a form of vitamin B3 and another building block for NAD+, the energy-and-repair coenzyme. Your body converts it through salvage pathways (possibly passing through NMN on…

NRF2 is your cells' emergency chief for oxidative stress. It is a transcription factor (a protein that switches genes on) that, once activated, turns on a whole defense program:…

NT-proBNP (N-terminal pro-B-type natriuretic peptide) is the inactive piece snipped off proBNP when your heart-muscle cells are stretched, by high pressure in the ventricle wall…

Nuclear pore complex (NPC) aging is the slow breakdown of the giant protein gates in your cell's nucleus over time. These pores (about 120 MDa each) perforate the nuclear…

The number needed to treat (NNT) is the average number of patients you must treat for one extra patient to benefit, versus a control. Laupacis, Sackett, and Roberts introduced it…

The oldest-old is the term for people aged 85 and over. It is the fastest-growing slice of most high-income populations. This group is remarkably mixed in how they fare. A…

EPA and DHA are the two key omega-3 fats. EPA is 20:5n-3; DHA is 22:6n-3. Both are long-chain polyunsaturated fats, found mainly in oily fish and fish oil (or algae supplements,…

The Omega-3 index is a blood test. It is the combined amount of two omega-3 fats, EPA and DHA, as a percentage of all the fatty acids in your red-blood-cell membranes. Because…

OMICmAge is a biological-age clock read from your DNA methylation. The clever part: it is trained to also reflect your proteins, metabolites, and routine lab values, without…

One-carbon metabolism is a linked set of chemical cycles (the folate and methionine cycles) that shuttle single carbon atoms around your cells. Your body uses those carbons to…

The one-repetition maximum (1RM) is the heaviest load you can lift through a full range of motion, for one all-out rep with proper form. It is the gold-standard measure of your…

The oral microbiome is the community of roughly 700 bacterial types in your mouth. They live on your teeth, gums, tongue, and lining. One species stands out: Porphyromonas…

Orexin-A and orexin-B are two excitatory brain signals (neuropeptides). They are also called hypocretin-1 and hypocretin-2. A small cluster of neurons in your hypothalamus makes…

Overtraining syndrome (OTS) sits on a continuum with functional overreaching (FOR) and non-functional overreaching (NFOR), per the ECSS/ACSM consensus. It is a maladaptive state…

Oxidative stress is an imbalance in your cells. On one side are reactive oxygen species (ROS). On the other are your body's antioxidant defenses. When ROS outpace the defenses,…

Oxidized LDL (oxLDL) is LDL that has been chemically altered by oxidation. Both its fats and its main protein (apolipoprotein B-100) get modified. This usually happens in your…

β-oxidation is the main way your mitochondria burn fat for energy. It chops a fatty acid into two-carbon pieces (acetyl-CoA), one cycle at a time. Each cycle runs four steps:…

p-tau217 is the tau protein phosphorylated at threonine 217. It is the most Alzheimer-specific plasma biomarker available right now. Its levels rise early along the amyloid…

p16INK4a is a brake on the cell cycle (a cyclin-dependent kinase inhibitor), made from the CDKN2A locus. It blocks CDK4/6, which halts the cell cycle and locks the cell into…

p21, encoded by the CDKN1A gene (cyclin-dependent kinase inhibitor 1A), is a strong brake on the cell cycle. It blocks cyclin-CDK complexes, especially CDK2. That enforces a…

p38 MAPK (p38 mitogen-activated protein kinase) is a stress-activated enzyme. It has four versions (α, β, γ, δ), with p38α the main, best-studied one. Upstream kinases (MKK3 and…

p53 is a tumor-suppressor protein, made from the TP53 gene. It acts as a master switch (a transcription factor) in your cell's response to stress, such as DNA damage, low oxygen,…

p62 (made by the SQSTM1 gene) is a multitasking 'adaptor' protein, best known as a selective receptor for autophagy, your cells' recycling system. It grabs cargo that has been…

Parasympathetic activation means engaging your 'rest-and-digest' nervous system. It is the calm-down branch of your autonomic nervous system. It works mainly through the vagus…

Parkin, encoded by the PRKN gene (formerly PARK2), is an E3 ubiquitin ligase. It is a RING-between-RING type. It sits at the center of mitochondrial quality control. In the…

PARP1 (poly(ADP-ribose) polymerase 1) is a nuclear enzyme. It is a central sensor of DNA damage, especially single-strand breaks. When activated, it cleaves NAD+. Then it…

Partial reprogramming tries to rejuvenate your cells without erasing what they are. It uses brief or low-dose 'Yamanaka factors' to roll cells back toward a younger state. But it…

PCGrimAge applies the same noise-reduction trick to the GrimAge clock. (The trick comes from Higgins-Chen et al., 2022.) The result is a more technically stable version of one of…

PCPhenoAge is a technically refined version of the DNAm PhenoAge clock, introduced by Higgins-Chen and colleagues (2022). The upgrade: it runs principal-component (PC) regression…

PCSK9 is both a gene and a hot drug target for lowering cholesterol. The protein (a serine protease made by your liver) latches onto the LDL receptor and sends it to be destroyed…

Peptide therapy uses short chains of amino acids, often injected, to try to modulate something in your body. Common targets are growth hormone (with peptides like sermorelin and…

These are PET scans that let doctors see Alzheimer's-related proteins in a living brain. Amyloid PET uses tracers (florbetapir, florbetaben, flutemetamol, all FDA-approved) to…

PET-FDG imaging maps where your body uses glucose. It uses a radioactive sugar tracer (18F-fluorodeoxyglucose), usually paired with a low-dose CT for anatomy (PET/CT). The…

PFAS ('per- and polyfluoroalkyl substances') are a class of thousands of synthetic chemicals with extremely stable carbon-fluorine bonds. That stability makes them persist in the…

PGC-1α is the master switch for building new mitochondria, your cells' power plants. It is a 'co-activator', meaning it cannot grab DNA itself; instead it teams up with other…

Pharmacogenomics is the study of how your genes change the way you respond to drugs, both how well they work and how toxic they are. The genes that matter most code for…

PhenoAge is a composite measure of your biological age. Levine and colleagues developed it in 2018. The original version is blood-based. It blends nine clinical markers with your…

Serum phosphate measures the inorganic phosphate floating in your blood. Its level reflects a balance between what your gut absorbs, what your kidneys hold onto, and what moves…

Photobiomodulation, often called red light therapy, shines low-level red and near-infrared light on tissue. Most clinical devices use about 600 to 900 nm. Some research extends…

The PI3K/AKT pathway is a central signaling line inside your cells. It is switched on by receptor tyrosine kinases (including the insulin and IGF-1 receptors), by…

PINK1 (PTEN-induced kinase 1) is a kinase that sits in your mitochondria and acts as a damage sensor. In a healthy mitochondrion, with an intact membrane voltage, PINK1 is pulled…

Pioglitazone is a diabetes drug (a thiazolidinedione) that makes your body more sensitive to insulin. It works by activating a receptor called PPARγ, which helps fat cells mature…

Plasma cells are fully matured B cells, the body's antibody factories. They drop their B-cell surface markers (including CD79, which partners the B-cell receptor) and ramp up two…

Plasmapheresis is the umbrella term for procedures that separate the plasma from the cells in your blood, outside your body. The technique varies. The plasma can be filtered and…

Plyometrics are explosive movements (jumps, hops, bounds, throws) that exploit the stretch-shortening cycle. In that cycle, a fast eccentric load primes a powerful concentric…

PM2.5 is airborne particles 2.5 micrometers across or smaller. They come mostly from combustion: vehicle exhaust, power plants, wood burning, and industry, plus secondary…

pNN50 is a time-domain measure of heart rate variability (HRV). It is the percentage of consecutive normal heartbeat intervals (NN, or R-R pairs) that differ by more than 50 ms.…

A polygenic risk score (PRS) sums up your genetic risk for a trait across many small DNA variants (SNPs). Each variant gets a weight, usually drawn from big genome-wide studies…

Polypharmacy usually means taking five or more medications at once. (Thresholds vary; some use 4 or more, and 'hyperpolypharmacy' is usually 10 or more.) It is not the same as…

Polyphenols are a huge, diverse group of plant compounds, over 8,000 of them. They are all built around aromatic rings carrying hydroxyl groups. The major subclasses include…

Polysomnography (PSG) is the gold-standard sleep study, done overnight in a lab. It records many channels at once: brain waves (EEG), eye movements (EOG), muscle activity (EMG),…

Polyvagal theory, proposed by Stephen Porges in 1995, makes a claim about your vagus nerve. It says two distinct vagal branches evolved in mammals: a newer 'ventral-vagal'…

A postbiotic is a preparation of dead microbes or their parts that still benefits your health. That is the ISAPP 2021 consensus definition. Here is the key difference from…

Postprandial glucose is your blood sugar after a meal. It often peaks within 30 to 90 minutes (around 60 minutes for mixed meals), then drifts back toward your fasting level.…

A prebiotic is food for your good gut microbes. The official definition comes from ISAPP (the International Scientific Association for Probiotics and Prebiotics). It is a…

The prefrontal cortex (PFC) is the front part of your brain that runs your 'executive' functions: working memory, mental flexibility, impulse control, and planning ahead. (It…

Presenilin 1 (PSEN1) and presenilin 2 (PSEN2) are nine-pass membrane proteins. They form the catalytic core of the gamma-secretase complex, together with nicastrin, APH-1, and…

ProAge and similar 'proteomic age' clocks estimate your biological age from the levels of hundreds to thousands of proteins in your blood. The proteins are measured by…

Probiotics are live microbes that, given in large enough amounts, bring a health benefit to the host. WHO/FAO set that definition in 2001. ISAPP reaffirmed it in 2014 (Hill et…

Progressive overload is the principle of gradually increasing your training demands, to keep driving adaptation. You can increase the load, the volume, the density, the range of…

Prolonged fasting means going without food for roughly 48 hours up to several days. During it, you take only water, electrolytes, and sometimes minimal calories. Once your…

Protein carbonylation is a permanent kind of oxidative damage to your proteins. It happens when carbonyl groups (aldehydes or ketones) get stuck onto a protein's side chains,…

Protein crosslinks are covalent bonds that join two protein molecules, or two parts of the same protein. They can form on purpose, by enzymes (as in collagen maturing). Or they…

Proteostasis (short for protein homeostasis) is the network that keeps your proteins working. It controls the whole life cycle of a protein: making it, folding it, moving it, and…

Prostate-specific antigen (PSA) is an enzyme (a kallikrein-family serine protease) made almost only by prostate cells. Its normal job is to liquefy semen, but it leaks into your…

Pterostilbene is a close cousin of resveratrol (a dimethylated stilbene). It is found naturally in blueberries, grapes, and Indian kino (Pterocarpus marsupium) heartwood. Two…

Pulse wave velocity (PWV) measures how fast the pressure wave from each heartbeat travels along your arteries. It is the non-invasive gold standard for arterial stiffness. The…

Pulsed electromagnetic field therapy (PEMF) sends low-frequency, low-strength pulsed magnetic fields into your tissue. It usually works through a flat coil, at frequencies from 1…

Pyroptosis is a highly inflammatory form of programmed cell death. The executioners are 'gasdermin' proteins, especially gasdermin D (GSDMD). Inflammatory caspases cut GSDMD. (In…

A Quality-Adjusted Life Year (QALY) is one year of life, weighted by your health-related quality of life. A score of 1.0 means one year in perfect health, and 0 means death.…

Quercetin is a flavonoid. You find it in onions, apples, capers, and berries. It has antioxidant and anti-inflammatory activity. It is being studied as a senolytic. (A senolytic…

Radon-222 is a colorless, odorless, naturally occurring radioactive noble gas. It forms when uranium-238 decays in soil and rock, and it builds up in basements and ground-floor…

A randomized controlled trial (RCT) is an experiment in which participants are assigned to an intervention or a control group by chance. It is the most reliable way to tell…

Rapamycin (also called sirolimus) is a drug that blocks mTORC1, the cell's main growth switch. It is a macrolide, first approved to stop the immune system from rejecting kidney…

Rate of force development (RFD) is the change in muscle force per unit of time (in N/s). It captures how fast you can express maximal force, which is a key part of power,…

The rate of living theory proposes that an animal's lifespan is inversely tied to its mass-specific metabolic rate. In short: the faster it burns energy, the sooner it dies. Max…

RDW (red cell distribution width) measures how much your red blood cells vary in size. Lab machines report it as a percentage, and the normal range is about 11.5 to 14.5%. A high…

Reactive oxygen species (ROS) are unstable molecules that contain oxygen. The main ones are superoxide, hydrogen peroxide, and hydroxyl radicals. Your cells make them in several…

A readiness score is a daily index defined by each vendor. Devices like Oura and Garmin made it popular (Garmin's version is branded Training Readiness or Body Battery). Whoop's…

A recovery score is a generic category of vendor-defined composite metrics. Each one tries to estimate how well your body has recovered from earlier strain. The branding differs…

Regenerative medicine builds therapies to repair, replace, or regrow damaged cells, tissues, and organs. Its tools are varied. They include stem-cell transplants, tissue…

The reliability theory of aging borrows math from engineering to explain why you age. Leonid and Natalia Gavrilov advanced it in the early 1990s. It models an organism as a…

REM sleep is named for its rapid eye movements. It is a distinct sleep stage with four signatures. Your eyes dart quickly. You dream vividly. Your brain activity is near-waking.…

Remnant cholesterol is the cholesterol packed inside triglyceride-rich lipoprotein remnants. When you are fasting, those are mainly VLDL and IDL; after meals, chylomicron…

In gerontology, physical resilience is your capacity to bounce back after an acute health hit. The hit could be an illness, surgery, fall, bereavement, or hospital stay. Whitson…

The respiratory exchange ratio (RER) is the ratio of carbon dioxide you produce (VCO₂) to oxygen you consume (VO₂) per unit time. At rest and during moderate aerobic effort, it…

Resting heart rate (RHR) is your heartbeats per minute at full rest. It is ideally measured lying down after several minutes of quiet rest, or right when you wake. It is swayed…

Resting metabolic rate (RMR) is the energy you burn at complete rest, just to keep your core systems running. (It is sometimes used interchangeably with basal metabolic rate, or…

Resveratrol is a stilbene polyphenol, found in grape skins, red wine, and Japanese knotweed. It is studied as a possible sirtuin (SIRT1) activator and AMPK modulator, with…

Retatrutide (LY3437943) is an investigational once-weekly injectable peptide from Eli Lilly. It activates three receptors at once: the GLP-1 receptor (GLP-1R), the GIP receptor…

RetinaAge is a biological-age clock built from retinal fundus photographs. A deep-learning model is trained to predict your age from the features of your optic disc, fovea, and…

Optical coherence tomography (OCT) takes ultra-detailed cross-section images of your retina, down to the micrometer. It lets doctors measure the thickness of retinal layers, like…

Reverse T3 (3,3',5'-triiodothyronine) is the inactive twin of T3. (T3 is the thyroid hormone that drives your metabolism.) It forms when an enzyme called D3 (5-deiodinase type 3)…

Reps in Reserve (RIR) is an autoregulation method for setting and grading how hard you train with weights. You estimate, at the end of a set, how many more reps you could have…

RMSSD (Root Mean Square of Successive Differences) is a time-domain measure of heart rate variability (HRV). It is the square root of the mean of the squared differences between…

Roseburia is a genus of bacteria that make butyrate. (Butyrate is a beneficial gut fat.) It belongs to the Lachnospiraceae family, part of the Firmicutes. Its best-studied…

Rate of perceived exertion (RPE) is a subjective scale for how hard exercise feels to you. The two most common versions are the 6-to-20 Borg scale and the 0-to-10 modified scale.…

S6K1 is a key worker downstream of mTORC1, your cells' growth switch. Its full name is ribosomal protein S6 kinase 1 (gene RPS6KB1). It is an enzyme that drives protein-making.…

SA-β-Gal (senescence-associated β-galactosidase) is an enzyme activity you can detect at pH 6.0. It reflects the swollen lysosomes and extra β-galactosidase (made by the GLB1…

SAM (S-adenosylmethionine) is your body's main methyl-group donor. It is the molecule that hands out the chemical tags used to mark DNA, histones, neurotransmitters, and fats.…

Sarcopenia is the age-related loss of your skeletal muscle mass, strength, and function. Several things drive it: anabolic resistance (muscle responds less to protein),…

Sarcopenic obesity is having two problems at once: low muscle mass or strength (sarcopenia) plus too much body fat. The combo is worse than either alone. Excess fat ramps up…

The senescence-associated secretory phenotype (SASP) is the cocktail of molecules that senescent ('worn-out') cells pump out into the tissue around you. It includes cytokines,…

Satellite cells are the resident stem cells of your muscle. They lie dormant between the muscle-fiber membrane (the sarcolemma) and its outer sheath (the basal lamina), and you…

A Finnish sauna is a dry-heat bath, typically 80 to 100°C with low humidity, used as a passive heat-stress tool. An acute session raises your core temperature and produces a…

SDNN (Standard Deviation of NN intervals) is a time-domain measure of heart rate variability (HRV). It captures the overall spread of your normal heartbeat intervals. Per HRV…

Selenium is built into proteins as the amino acid selenocysteine, often called the 21st amino acid. That forms a class of enzymes called selenoproteins, with 25 encoded in the…

Semaglutide is a long-acting GLP-1 receptor agonist. It is approved for type 2 diabetes (as Ozempic and Rybelsus). It is also approved for chronic weight management (as Wegovy).…

A senescent-cell vaccine is an attempt to train your immune system to find and kill senescent ('zombie') cells, much like a cancer vaccine trains it against tumors. Suda and…

Senolytic therapy uses drugs or natural compounds to selectively kill senescent cells. These 'zombie' cells build up in you with age and leak a toxic mix (the SASP) of…

Senolytics are drugs that hunt down and kill senescent "zombie" cells, the worn-out cells that pile up in your tissues with age. They spare healthy cells. They work by exploiting…

Senomorphics are compounds that quiet senescent cells, rather than killing them. (They are also called senostatics.) Specifically, they tone down the harmful molecules these…

Sermorelin is a synthetic 29-amino-acid copy of your body's growth hormone-releasing hormone (GHRH 1-29). It prompts your pituitary to release growth hormone (GH) in natural…

Sestrins (SESN1, SESN2, SESN3) are stress-triggered proteins, conserved across evolution. They turn down mTORC1 (a master growth switch) and turn up AMPK (an energy sensor), the…

SGLT2 inhibitors (the 'gliflozins', like empagliflozin and dapagliflozin) block a kidney transporter called sodium-glucose cotransporter 2. That makes you pee out excess glucose.…

SHBG (sex hormone-binding globulin) is a protein your liver makes that grabs and carries sex hormones in your blood. It binds about 44% of your testosterone and 30 to 60% of your…

The shelterin complex is a six-protein assembly. The six are TRF1, TRF2, TIN2, TPP1, POT1, and RAP1. It constantly coats the TTAGGG repeats at your chromosome ends. That stops…

Shift work is any schedule that pushes your working hours outside the usual 7am-to-6pm window, including fixed nights and rotating shifts. It chronically misaligns your behavior…

Short-chain fatty acids (SCFAs) are the helpful byproducts your gut bacteria make. The main three are acetate, propionate, and butyrate. They form when anaerobic gut microbes…

A single-nucleotide polymorphism (SNP, said 'snip') is a germline variation at a single base-pair position. It exists where two or more nucleotide alleles occur in the population…

Sirtuins are a family of enzymes that depend on NAD⁺ to remove chemical tags from proteins. The three most studied for longevity differ sharply in where they work and what they…

Sirtuins are a family of seven enzymes (SIRT1 through SIRT7) that act as metabolic sensors. They strip chemical tags off other proteins (mainly acetyl groups) to tune metabolism,…

The sit-rise test measures your ability to lower yourself to the floor and stand back up, using as little support as possible. It is scored from zero to ten, with points deducted…

Dermoscopy (also called dermatoscopy) uses a handheld lens at about 10x magnification. With polarized or immersion light, it reveals pigment patterns and tiny blood vessels under…

Sleep apnea is a disorder of repeated breathing pauses or shallow breaths (apneas and hypopneas) during sleep. The most common form is obstructive sleep apnea, from your upper…

Sleep architecture is how your sleep stages are organized across the night. A typical night runs through four to six 90-minute cycles. Each cycle moves through N1, N2, N3 (deep,…

Sleep debt is the running shortfall between the sleep your body needs and the sleep you actually get, night after night. It builds up bit by bit. Restricting sleep to 6 hours a…

Sleep efficiency is the percentage of your time in bed that you actually spend asleep. You calculate it as total sleep time divided by time in bed. In adults, a value of 85% or…

Sleep latency is how long it takes you to fall asleep, from lights-out to the first moment of sleep. It is usually measured in minutes during a sleep study (polysomnography). A…

The two-process model, proposed by Alexander Borbély in 1982, explains sleep and wake as two forces working together. Process S is homeostatic sleep pressure. It builds up while…

Sleep regularity is how consistent your sleep-wake timing is from day to day. It is scored by the Sleep Regularity Index (SRI), which runs from −100 to 100. A 0 means totally…

Sleep spindles are short bursts of rhythmic brain activity, in the 11-16 Hz range. On an EEG, they look like waxing-and-waning 'sigma-band' waves, and they define stage N2 of…

Small dense LDL (sdLDL) is a smaller, denser subtype of LDL cholesterol particles (under about 25.5 nm across). They form mainly when you have high triglycerides and insulin…

Social determinants of health (SDoH) are the non-medical conditions in which you are born, grow, live, work, and age. They include income, education, job quality, housing,…

Social jetlag is the chronic mismatch between your internal body clock and the sleep-wake schedule your obligations (work, school) impose. It is measured as the difference in the…

Somatic mutations are DNA changes that arise in your body cells after conception, not in the germline. They affect only the descendants of the cell where they happen. Every cell…

Soy isoflavones are plant compounds (polyphenols) that act as weak estrogens. They look structurally similar to your body's estrogen (17β-estradiol). They are concentrated in…

Specialized pro-resolving mediators (SPMs) are your body's 'stop' signals for inflammation. They are bioactive fats made from polyunsaturated fatty acids. Lipoxins come from…

Spermidine is a naturally occurring polyamine, found in wheat germ, aged cheese, soy, and mushrooms, so you already eat some. The content varies a lot by source and processing.…

Statins (drugs like atorvastatin and rosuvastatin) lower your cholesterol by blocking a liver enzyme called HMG-CoA reductase and ramping up the receptors that pull LDL out of…

Stem cell exhaustion is the age-related decline of your tissue-resident stem cells. They drop in number, function, and regenerative power. Several things drive it. There is…

The stem cell niche is the local microenvironment that controls a stem cell. It is made of neighboring support cells, blood vessels, the extracellular matrix, soluble signals,…

Strength training is structured exercise. You load your muscles against resistance. That can be free weights, machines, bands, or your own bodyweight. The load drives two things:…

Stroke volume is the amount of blood your left ventricle pumps out per heartbeat. At rest in healthy adults, that is about 60 to 100 ml. In elite endurance athletes at peak…

Successful aging is a framework introduced by John Rowe and Robert Kahn (1987, Science), and elaborated in 1997. It distinguishes 'usual' aging, where outside factors pile on top…

Sulforaphane is a plant compound (an isothiocyanate). It forms when you chew or chop broccoli, broccoli sprouts, and other crucifers. It activates a pathway called Nrf2. That…

A supercentenarian is a person verified to have reached the age of 110 or more. The 110-plus threshold and the term were popularized mainly by L. Stephen Coles, founder of the…

The suprachiasmatic nucleus (SCN) is a paired structure in your hypothalamus, sitting just above the optic chiasm, with about 20,000 neurons per side. It is the master circadian…

Sympathetic dominance is when your nervous system gets stuck in 'go' mode. The fight-or-flight (sympathetic) side chronically outweighs the rest-and-digest (parasympathetic)…

Synaptic plasticity is the activity-driven change in the strength of connections between your neurons. It is considered the cellular basis of learning and memory. The classic…

SystemsAge is a methylation-based biological-age clock that looks at multiple body systems. Sehgal et al. introduced it (2025, Nature Aging, Levine lab). From a single blood…

T-cell exhaustion is a worn-out, underperforming state that your antigen-specific T cells (mainly CD8+ killer T cells) fall into when an antigen sticks around too long, as in…

TA-65 is a proprietary, purified extract enriched in cycloastragenol, from Astragalus membranaceus. T.A. Sciences markets it (under license from Geron), and sells it to you as a…

Tau is a protein that normally stabilizes the internal skeleton of your nerve cells, by binding to microtubules. In Alzheimer's and related 'tauopathies', it goes wrong. It gets…

Taurine is a sulfur-containing amino acid, though it is not used to build proteins. Your body makes it from cysteine, through the cysteine sulfinic acid pathway. You also get a…

Telomerase is an enzyme that rebuilds the caps on your chromosome ends. Technically, it is a ribonucleoprotein 'reverse transcriptase'. It pairs a protein part (TERT) with an RNA…

Telomeres are the protective caps on the ends of your chromosomes, a bit like the plastic tips on shoelaces. They are made of a short DNA sequence (TTAGGG) repeated over and…

Telomere attrition is the gradual shortening of the protective caps at your chromosome ends. (Those caps are repeats of the sequence TTAGGG.) They shorten a little with each cell…

Tendon stiffness describes how much force a tendon transmits per unit of stretch (force divided by length change, usually in N/mm). A related property, Young's modulus, adjusts…

TERT and TERC are the two core parts of telomerase. Telomerase is the enzyme that rebuilds the protective caps (telomeres) on your chromosomes. TERT (telomerase reverse…

TERT (telomerase reverse transcriptase) is the business end of telomerase, the enzyme that rebuilds your chromosome caps (telomeres). In most adult human tissues, TERT is…

Testosterone is the main androgen (male sex hormone). In men, it is made mostly by Leydig cells in the testes. In women, the ovaries and adrenals make smaller amounts. It…

If you have diagnosed hypogonadism, testosterone replacement therapy (TRT) restores the hormone. (Hypogonadism means low blood testosterone plus symptoms.) It is given via gels,…

TET1, TET2, and TET3 are enzymes that erase DNA methylation marks, step by step. (They are iron- and alpha-ketoglutarate-dependent dioxygenases.) They oxidize a methylated DNA…

TFEB (transcription factor EB) is a basic helix-loop-helix protein. It works as a master switch for autophagy and for building lysosomes (the cell's recycling centers that keep…

TGF-β (transforming growth factor β) signaling starts when TGF-β proteins (TGF-β1, β2, β3) bind a receptor complex (TβRII paired with TβRI). That complex tags messenger proteins…

Therapeutic plasma exchange (TPE) is a specific form of plasmapheresis. In each session, roughly one to one-and-a-half plasma volumes are removed from your blood. That plasma is…

Thymic involution is the slow replacement of your thymus tissue with fat. It starts in early childhood and speeds up at puberty. As it progresses, the thymus makes fewer fresh…

Thymosin α-1 (Tα1) is a 28-amino-acid peptide, cut from a precursor (prothymosin α), naturally made by the epithelial cells of your thymus. It tunes both innate and adaptive…

Anti-TPO and anti-thyroglobulin (TgAb) are antibodies. Your immune system makes them against your own thyroid enzymes. They are the main blood markers of autoimmune thyroid…

Time-restricted eating (TRE) confines your daily food intake to a consistent window, typically 6 to 10 hours. That leaves 14 to 18 hours of fasting. The concept came from Satchin…

Tirzepatide is a once-weekly drug. It switches on two gut-hormone receptors at once: GIP and GLP-1. It is approved for type 2 diabetes (sold as Mounjaro). It is also approved for…

TMAO (trimethylamine-N-oxide) is a small compound your gut bacteria help make. They convert dietary choline, phosphatidylcholine, and L-carnitine (abundant in red meat, eggs, and…

TNF-α (tumor necrosis factor alpha) is a powerful pro-inflammatory signal (a cytokine). It is made mostly by immune cells called macrophages and monocytes, when they sense…

Tobacco smoking is one of the strongest known accelerators of biological aging. And it is one you can actually change. It works through at least three mechanisms. First, it…

Toll-like receptors (TLRs) are ten receptors, on the cell surface and inside endosomes, that form a primary sensing layer of your innate immunity. The surface TLRs (TLR1, TLR2,…

Trained immunity is the idea that your innate immune cells can 'learn'. The concept comes mainly from Mihai Netea and colleagues. It means your fast-response immune cells (mainly…

Transferrin saturation (TSAT) is the share of iron-binding seats on transferrin, your blood's main iron-carrier, that are filled with iron. You calculate it as (serum iron ÷…

T regulatory cells (Tregs) are a specialized subset of CD4+ T cells, defined by a master protein called FOXP3. Their job is to suppress excessive immune responses and keep your…

TREM2 (triggering receptor expressed on myeloid cells 2) is a receptor that sits across the cell membrane. In the brain, almost only microglia (the brain's immune cells) carry…

Triglycerides are the main way your body stores fat, from your diet and from what your body makes. They travel in your blood inside fat-carrying particles. The main ones are…

Thyroid-stimulating hormone (TSH) is released by your pituitary gland. It controls how much thyroid hormone you make, through negative feedback from the circulating thyroid…

The TyG index is a quick stand-in for insulin resistance. You calculate it as ln(fasting triglycerides [mg/dL] × fasting glucose [mg/dL] ÷ 2). Simental-Mendía et al. proposed it…

Type I interferons are your body's first-line antiviral alarm signals. The main ones are IFN-α (many subtypes) and IFN-β. Almost any cell with a nucleus can release them when it…

Your skeletal muscle has two broad fiber types: Type I (slow) and Type II (fast). They differ in their myosin type, metabolism, and contraction speed. Type I fibers are…

The ubiquitin-proteasome system (UPS) is one of your cells' main ways to destroy proteins on purpose. It targets short-lived, misfolded, or regulatory proteins, and it…

The ULK1 complex is a four-part kinase assembly. It includes ULK1 (Unc-51-like autophagy-activating kinase 1), the scaffold FIP200, and two regulatory subunits, ATG13 and ATG101.…

Uncoupling proteins (UCPs) are carriers in your inner mitochondrial membrane that release the proton gradient as heat instead of capturing it as ATP. The best-known is UCP1,…

The unfolded protein response (UPR) is a rescue program your cells run when misfolded proteins pile up in the endoplasmic reticulum (ER). Three sensors kick it off: IRE1alpha,…

Uric acid is the end product of breaking down purines in your body. Your liver makes it (via an enzyme, xanthine oxidase), and you clear it mostly through your kidneys (~70%),…

The urine albumin-to-creatinine ratio (UACR) measures how much albumin is leaking into your urine, divided by your urinary creatinine (which corrects for how hydrated you are). A…

Urolithin A is a compound your gut bacteria make. They produce it by transforming ellagitannins and ellagic acid, polyphenols found in pomegranates, walnuts, and berries, using…

Photoaging is the cumulative skin damage from chronic exposure to the sun's ultraviolet (UV) light. It is distinct from intrinsic aging (chronoaging). UVA (320 to 400 nm) reaches…

Vaccines work less well as you age, and several immune changes pile up to cause it. You have fewer fresh (naive) T and B cells, weaker germinal-center reactions, shorter-lived…

Vagal tone is the baseline activity of your vagus nerve. The vagus is the main parasympathetic pathway, connecting your brainstem to organs like your heart, lungs, and gut.…

Vascular calcification is the buildup of calcium-phosphate mineral (hydroxyapatite) in your artery walls. It is an active, cell-controlled process. It is not the passive…

Vascular dementia is cognitive decline severe enough to disrupt your daily life, caused by problems with the brain's blood supply. It is the second most common dementia after…

Visceral adipose tissue (VAT) is the metabolically active fat packed around your abdominal organs. It is different from the fat under your skin (subcutaneous fat). VAT is…

Vitamin B12 (cobalamin) and folate (vitamin B9) are essential helper molecules. They work in 'one-carbon metabolism'. B12 is needed for two enzymes. One is methionine synthase.…

25-hydroxyvitamin D (25-OH-D, or calcidiol) is the main circulating form of vitamin D, and the standard blood test for your vitamin D status. Your liver makes it by adding a…

Vitamin E is a family of eight fat-soluble molecules. There are four tocopherols (α, β, γ, δ) and four tocotrienols (α, β, γ, δ). They share a 'chromanol' ring but differ in…

Menaquinone-7 (MK-7) is a long-chain form of vitamin K2. Its side chain has seven isoprene units, which gives it a longer half-life than vitamin K1 (phylloquinone) or MK-4, so it…

VO2max is the maximum rate at which you can use oxygen during intense exercise. It is usually expressed in mL/kg/min. By the Fick principle, it equals your oxygen delivery…

Wake After Sleep Onset (WASO) is the total time you spend awake during the night. It counts the minutes after you first fall asleep, but before your final wake-up. It sums up all…

White matter hyperintensities (WMH) are patches that light up abnormally bright on certain brain MRI scans (T2-weighted and FLAIR), within the brain's white matter. They are not…

Whole-body cryotherapy (WBC) blasts your body with extreme cold air, typically −100 to −140°C, for 2 to 4 minutes in a chamber. That is different from cold-water immersion (CWI),…

Whole-body MRI (WB-MRI) scans you from head to pelvis (brain, neck, chest, abdomen, pelvis) in one session, with no radiation. It takes about 45 to 90 minutes and shows soft…

Whole-genome sequencing (WGS) reads every letter of your DNA, in both the nuclear genome and the mitochondria. Older SNP chips miss a lot. WGS can spot rare changes:…

The Wim Hof method mixes three things. First, cycles of fast, deep breathing (like hyperventilation). Second, breath holds. Third, gradual cold exposure. The Dutch athlete Wim…

Wnt signaling is a family of ancient cell-to-cell communication pathways. It starts when secreted Wnt proteins bind 'Frizzled' receptors on your cells. The most-studied branch is…

WRN is a gene that makes a DNA-repair enzyme, part of the RecQ helicase family. It has both helicase and exonuclease activities. It works in several repair pathways: base…

Xenohormesis is the idea that animals gain from the stress-response molecules made by stressed plants and microbes. You sense these molecules as cues that the environment is…

The Yamanaka factors are four transcription factors: OCT4, SOX2, KLF4, and c-MYC (together, OSKM). Shinya Yamanaka identified them in 2006. He showed they are enough to reprogram…

Zone 2 training is sustained aerobic exercise at or just below your first lactate threshold (LT1, around 1.5 to 2.0 mmol/L). That is often roughly 60 to 70% of your max heart…