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

CATEGORY: SLEEP & RECOVERY

Sleeping the recommended number of hours did not cancel out the risk that came with a shifting schedule. Among 72,269 UK adults aged 40 to 79, those whose bedtimes and wake times moved most from day to day carried a 26% higher risk of a major cardiovascular event over roughly eight years than people who kept steady hours. That category covers heart attack, stroke, heart failure and death from heart disease.¹ For the most irregular sleepers, enough total sleep left the risk 19% higher anyway.

A Week on the Wrist, Then Eight Years of Records

Participants, none of whom had a history of major cardiovascular events, wore a wrist activity tracker around the clock for one week. From that week of recordings, researchers calculated each person’s Sleep Regularity Index, a 0-to-100 score for how consistent sleep and wake times are from one day to the next. The score works like a report card for the 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. That week served as a snapshot of habitual patterns, nothing more. The outcomes came later: participants were followed for an average of 7.8 years through hospital records and death registries, during which 4,887 major cardiovascular events occurred. Those events struck 7.8% of the most irregular sleepers and 6.2% of the regular sleepers.¹

Above 87 Counted as Regular, Below 72 as Irregular

Scores above about 87 counted as regular sleep, scores below about 72 as irregular, and the range between as moderately irregular. Set against regular sleepers, irregular sleepers carried 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 tracked with a 45% higher risk of heart failure, a 23% higher risk of heart attack and a 22% higher risk of stroke.

Enough Hours, Still 19% Higher

The researchers then asked whether sleeping the recommended amount could make up for an inconsistent schedule. Those recommendations run 7 to 9 hours a night for adults up to age 64, and 7 to 8 hours for people 65 and older. For moderately irregular sleepers, meeting them largely did the job, leaving no clear increase in risk. For the most irregular sleepers, it did not. Their risk stayed 19% higher even when total sleep was sufficient. In this study, when a person slept mattered in a way that how long they slept could not fully offset.

This was observational work, so it shows an association rather than proof of cause and effect. Age, sex, physical activity, diet, smoking, shift work and many other factors were accounted for, yet unmeasured differences between regular and irregular sleepers could still be at play. The link is biologically plausible: erratic timing pushes against the circadian rhythm, the internal 24-hour clock that helps regulate blood pressure, hormones and metabolism, rather like living in permanent mild jet lag.¹

Two other studies sit alongside it. A 2026 systematic review pooling three wearable-based studies of more than 150,000 adults put the most irregular sleepers at about 25% higher risk of a major cardiovascular event than the most regular.² An earlier American 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 too.

Key Takeaways

• Among 72,269 UK adults tracked for about eight years, the most irregular sleepers carried a 26% higher risk of heart failure, heart attack, stroke or cardiovascular death than those on steady schedules.
• Meeting recommended sleep-duration targets offset the added risk for moderately irregular sleepers but not for the most irregular ones, whose risk stayed 19% higher.
• 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.