Irregular Sleep Tracked With More Heart Events, Even When Sleep Was Long Enough

CATEGORY: SLEEP & RECOVERY

People whose bedtimes and wake times shifted the most from day to day had a 26% higher risk of heart attack, stroke, heart failure or death from heart disease over roughly eight years, compared with people who kept a steady sleep schedule, in a study of 72,269 UK adults aged 40 to 79.¹ The finding came with a twist: for the most irregular sleepers, getting the recommended amount of sleep did not erase the extra risk.

One Week of Wrist Tracking, 7.8 Years Follow-Up

Researchers gave participants—none of whom had a history of major cardiovascular events—a wrist activity tracker to wear around the clock for one week. From that week of recordings they calculated each person’s Sleep Regularity Index, a 0-to-100 score that measures how consistent your sleep and wake times are from one day to the next. Think of it as a report card for your body clock: someone who falls asleep and wakes at nearly the same times every day scores high, while someone whose schedule swings widely scores low. The week of tracking served as a snapshot of habitual sleep patterns; the health outcomes came later, as participants were followed for an average of 7.8 years through hospital records and death registries, during which 4,887 major cardiovascular events occurred. Major cardiovascular events occurred in 7.8% of the most irregular sleepers and 6.2% of the regular sleepers.¹

Scores Above 87 Regular, Below 72 Irregular

Scores above about 87 counted as regular sleep, scores below about 72 as irregular, and the range between as moderately irregular. Compared with regular sleepers, irregular sleepers had a 26% higher risk of a major cardiovascular event, and moderately irregular sleepers an 8% higher risk—with risk climbing in a near-straight line as regularity fell. Among the individual outcomes, irregular sleep was linked to a 45% higher risk of heart failure, a 23% higher risk of heart attack and a 22% higher risk of stroke.

Risk Stayed 19% Higher Despite Enough Sleep

The researchers also asked whether sleeping the recommended amount—7 to 9 hours a night for adults up to age 64, and 7 to 8 hours for those 65 and older—could make up for an inconsistent schedule. For moderately irregular sleepers, it largely did: those who met the sleep-duration guidelines no longer showed a clear increase in risk. For the most irregular sleepers, it did not—their risk remained 19% higher even when they got enough total sleep. In this study, when a person slept mattered in a way that how long they slept could not fully offset.

Adjusted for Shift Work, Still Not Causal Proof

This was an observational study, so it shows an association, not proof of cause and effect. The researchers adjusted for age, sex, physical activity, diet, smoking, shift work and many other factors, but unmeasured differences between regular and irregular sleepers could still play a role. The link is biologically plausible, though: erratic sleep timing pushes against the circadian rhythm—the internal 24-hour clock that helps regulate blood pressure, hormones and metabolism—much like living in a permanent state of mild jet lag.¹

Three Wearable Studies of More Than 150,000 Adults

A 2026 systematic review pooling three wearable-based studies of more than 150,000 adults found the most irregular sleepers had about a 25% higher risk of a major cardiovascular event than the most regular.² An earlier US study of nearly 2,000 adults followed about five years linked the most variable sleep timing to roughly double the risk.³ Both are observational, so they show a link, not cause.

Key Takeaways

• In 72,269 UK adults tracked for about eight years, the most irregular sleepers had a 26% higher risk of heart attack, stroke, heart failure or cardiovascular death than those with steady sleep schedules.
• Meeting recommended sleep-duration targets offset the added risk for moderately irregular sleepers, but not for the most irregular ones.
• The study was observational, so it shows an association rather than proof that irregular sleep causes heart problems.

References

1. Chaput JP, Biswas RK, Ahmadi M, Cistulli PA, Rajaratnam SMW, Bian W, St-Onge MP, Stamatakis E. Sleep regularity and major adverse cardiovascular events: a device-based prospective study in 72 269 UK adults. J Epidemiol Community Health. 2025;79(4):257–264. link
2. Ahmad AM, Kazi F, Arif S, et al. Sleep irregularity and major adverse cardiovascular events in adults: a systematic review and meta-analysis. SN Comprehensive Clinical Medicine. 2026;8(1):215. link.
3. Huang T, Mariani S, Redline S. Sleep irregularity and risk of cardiovascular events: the Multi-Ethnic Study of Atherosclerosis. Journal of the American College of Cardiology. 2020;75(9):991–999. link.