Social jetlag

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 midpoint of your sleep between free days and workdays. Wittmann, Dinich, Merrow, and Roenneberg introduced the term in 2006, measuring it in hours with the Munich Chronotype Questionnaire. About 69 to 70% of adults in industrialized countries have at least an hour of mismatch. 'Night owl' chronotypes get hit hardest, because social start times come earlier than their clocks prefer. Roenneberg et al. (2012, Current Biology) showed the stakes in a large European cohort. Social jetlag carried an odds ratio of 3.3 (95% CI 2.5 to 4.3) for being in the overweight group, independent of sleep duration. That was one of the first big human links between circadian mismatch and body fat. The proposed mechanisms all converge on metabolic trouble: HPA-axis dysregulation with high cortisol, autonomic activation, appetite-hormone shifts (more ghrelin, less leptin), worse insulin sensitivity, and less physical activity. The cardiovascular-risk evidence in humans is still mostly associational. Lab misalignment studies confirm acute physiological changes. But long-term randomized trials showing that fixing social jetlag improves hard outcomes are still lacking as of 2026.

Last reviewed: June 22, 2026

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