# Sleep regularity

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 random; 100 means perfectly identical days. The SRI basically asks: across a week of wrist-tracker data, how likely are you to be in the same state (asleep or awake) at any two moments exactly 24 hours apart? Unlike sleep duration (how long you sleep), the SRI captures whether you sleep at the same clock times each day, reflecting how stable your body clock is. The payoff is large. In a study of 60,977 UK Biobank participants followed 6.3 years (Windred et al., 2024), the most regular fifth had 20 to 48% lower all-cause death, 16 to 39% lower cancer death, and 22 to 57% lower cardiometabolic death than the least regular. And when both SRI and duration were tested together, duration added nothing on its own. A separate UK Biobank analysis (Cribb et al., 2023, n=88,975) confirmed a non-linear link: the lowest SRI percentile (score around 41) carried a 53% higher death risk than the median. The proposed mechanism: chronic irregularity throws your body clock out of sync, misaligning organ clocks with the brain's master pacemaker, which promotes inflammation, stress-hormone (HPA) dysregulation, autonomic dysfunction, and gut dysbiosis. But both studies are observational, so cause is not proven.

## Sources

- Windred DP, Burns AC, Lane JM, Saxena R, Rutter MK, Cain SW, et al.. (2024). Sleep regularity is a stronger predictor of mortality risk than sleep duration: A prospective cohort study. Sleep. https://doi.org/10.1093/sleep/zsad253
- Cribb L, Sha R, Yiallourou S, Grima NA, Cavuoto M, Baril AA, et al.. (2023). Sleep regularity and mortality: a prospective analysis in the UK Biobank. eLife. https://doi.org/10.7554/elife.88359
- Zhang C, Qin G. (2023). Irregular sleep and cardiometabolic risk: Clinical evidence and mechanisms. Frontiers in Cardiovascular Medicine. https://doi.org/10.3389/fcvm.2023.1059257

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_Canonical: https://longevity-switzerland.com/en/glossary/sleep-regularity · Part of Longevity Cities · Updated 2026-06-22_