Flavonoids

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 (catechins, epicatechins; tea, cocoa). Anthocyanins (berries, red cabbage). Flavanones (naringenin; citrus). Flavones (luteolin, apigenin; herbs). And isoflavones (genistein; soy). They work in several ways. They mop up reactive oxygen species, block NF-κB inflammation, and switch on Nrf2. And flavan-3-ols raise nitric oxide to improve blood-vessel function. The observational evidence is consistent. Higher intake tracks with lower heart and all-cause death. A dose-response meta-analysis of 39 cohorts (1.5 million people; Micek et al., 2021) found lower heart-disease risk. It was strongest for anthocyanins and flavan-3-ols. A 2025 UK Biobank analysis (Parmenter, Cassidy et al.) found that variety, not just amount, mattered. It went with 6 to 20% lower risk of death, heart disease, type 2 diabetes, and brain disease. Trial evidence is thinner. COSMOS (Sesso, Manson et al., 2022) tested 500 mg/day cocoa flavanols in 21,442 older US adults. Total cardiovascular events did not fall significantly. But cardiovascular death dropped 27%. COSMOS-Mind (Baker et al., 2022) found no cognitive benefit over three years. Bioavailability varies a lot by subclass and person, partly down to your gut microbes. And isolated supplements have not reproduced the benefits seen with whole-food diets.

Last reviewed: June 22, 2026

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