Irregular Sleep Timing Linked to Higher Cardiovascular Risk
A consistent sleep schedule may matter more for the heart than many people realize. In a large preliminary analysis presented for American Heart Association Scientific Sessions 2026, night-to-night changes in bedtime, wake time and sleep duration were linked to higher rates of serious cardiovascular events, including heart attack, stroke and heart failure.
The most striking pattern was not simply short sleep. It was inconsistency. People whose sleep timing shifted from night to night over roughly six months faced a 20% to 23% higher risk of major heart events, and every 29-minute increase in variability in sleep length was tied to a 24% higher risk of the combined cardiovascular outcome. The signal extended beyond broad risk estimates and into specific outcomes: the same increase in sleep-length variability was associated with a 29% higher risk of disease of the heart muscle and a 20% higher risk of heart failure.
Sleep regularity may be doing work that sleep duration alone does not capture.
Wearable Data From More Than 10,000 Adults
Researchers examined sleep data from 10,362 adults in the National Institutes of Health’s All of Us Research Program. The cohort contributed more than 1 million nights of sleep data, collected through wearable activity trackers while participants slept at home. Average age was 53, about 69% were women, and 81.6% self-reported as white adults. Black adults made up 4.6% of the sample, Asian adults 3.1%, and 10.7% identified as another race or did not report race. None had heart or metabolic disease at baseline.
Sleep was assessed across several dimensions. Investigators tracked total sleep time, sleep quality, sleep regularity, sleep timing and sleep cycles. Regularity captured how much bedtimes, wake times and sleep duration changed from one night to the next. Timing reflected the typical sleep window and its midpoint, a marker related to chronotype, the tendency toward being a night owl or an early bird.
The study design matters because it moves beyond a one-night snapshot. Sleep can look acceptable on a single evening while still being biologically erratic across a week, a month or an entire season. For cardiovascular physiology, that repeated variability may be more disruptive than people assume.
The Cardiovascular Signals Went Beyond Sleep Duration
The analysis found that greater variability in sleep timing over about six months was associated with a 20% to 23% higher risk of serious cardiovascular disease. Sleep duration instability carried its own burden. Each 29-minute rise in how much sleep length varied night to night was tied to a 24% higher risk of the combined cardiovascular outcome, along with a 29% higher risk of disease of the heart muscle and a 20% higher risk of heart failure.
A different pattern emerged for sleep architecture. Having a greater number of complete sleep cycles each night was associated with a 28% lower risk of atrial arrhythmia, a common irregular heartbeat. In contrast, an unusually long sleep cycle was linked to a 55% higher risk of heart attack or stroke.
These findings point to more than a simple hours-slept equation. Circadian misalignment can affect autonomic tone, blood pressure regulation, metabolic signaling and inflammatory pathways, all of which influence vascular stress. When sleep timing and sleep length swing unpredictably, the body may have to repeatedly re-adapt its internal clock, and that kind of physiological friction can plausibly worsen cardiovascular risk over time.
Why Bedtime Regularity May Matter at the Bedside
Lead investigator Nguyen Minh Tuan Viet, M.D., Ph.D., described sleep regularity as a practical target because many people can control it even when they cannot fully control sleep quality. Shift work and weekend schedule drift can push bedtime later and wake time later, creating a pattern of social jet lag that may be unfriendly to cardiovascular health.
Short, stable sleep is not the same as long, erratic sleep. A person can miss the mark on ideal duration and still preserve a predictable rhythm, while another may sleep long enough on average but shift hours frequently from one night to the next. From a clinical perspective, that difference matters because the cardiovascular system responds not only to how much sleep occurs, but to when it occurs and how consistently it is repeated.
This helps explain why regularity could be more than a wellness slogan. If circadian biology is chronically forced to recalibrate, blood pressure, glucose handling and vascular repair may all lose precision. Over months and years, those small disruptions can accumulate into measurable disease risk.
Caution Is Still Required Before Turning Association Into Advice
Marie-Pierre St-Onge, Ph.D., C.C.S.H., FAHA, who was not involved in the analysis, urged caution in interpreting the findings. She noted that the field has strong evidence linking insufficient sleep to cardiovascular risk factors, but causal evidence for sleep regularity itself remains incomplete.
The study is observational, so it cannot establish cause and effect. Wearable devices measured sleep stages at home rather than using brain-monitoring equipment in a sleep laboratory, which remains the reference standard for detailed sleep study. Even with statistical adjustment for age, sex, race, education, income, smoking, alcohol use, cancer and mental health conditions, residual confounding remains possible. People with unstable sleep schedules may also differ in work patterns, stress, caregiving demands, or other factors that could influence cardiovascular outcomes.
The preliminary nature of the abstract also matters. Findings presented at scientific meetings are not peer-reviewed in the same way as full journal manuscripts, and they should be treated as hypothesis-generating rather than definitive practice-changing evidence.
Still, the message is clinically intuitive. A regular bedtime, a consistent wake time and a stable sleep window may be worth preserving alongside the usual emphasis on sleep duration. The data suggest that the heart may respond not only to sleep quantity, but to the rhythm of sleep itself. Before routine cardiovascular prevention guidance can formally include sleep regularity, stronger longitudinal studies and mechanistic work will need to show whether the association holds when measured with more rigorous sleep phenotyping and whether improving regularity actually lowers event rates.