Uneven sleep was linked to heart trouble in 10,000 adults. It doesn't prove why.

A pattern across a million nights

Adults whose sleep varied more from night to night had a higher subsequent risk of cardiovascular events in a preliminary analysis released by the American Heart Association on Monday. The findings, drawn from more than a million nights of sleep, are due to be presented at the association's scientific meeting in Chicago on Nov. 6–9; they have not yet been peer-reviewed.newsroom

Researchers examined data from 10,362 participants in the National Institutes of Health's All of Us research program. Their sleep was measured with wearable devices over roughly six months, and they were followed for a median of 3.7 years. None had heart or metabolic disease at the start. The average participant was 53, and about seven in 10 were women.newsroom +1

What the numbers mean

For each 29-minute increase in night-to-night variation in sleep duration, the researchers reported a 24% higher relative risk of a combined outcome that included heart attack, stroke and heart failure. Changes in sleep timing were associated with a 20% to 23% higher risk of serious cardiovascular events.newsroom

Those figures describe differences between people with varying degrees of irregularity, not the effect of a single late night or a guaranteed personal risk. The release did not provide absolute event rates for these comparisons. The analysis accounted for factors including age, income, smoking and mental health conditions, but an observational study cannot rule out other explanations.newsroom

Earlier research and limits

The association is not entirely new. A 2025 study of 72,269 UK adults found that people with irregular sleep patterns had more major cardiovascular events than regular sleepers over eight years. A smaller 2020 NIH-supported study also linked irregular sleep to cardiovascular disease in adults aged 45 to 84. Both were observational.pubmed +1

Wearables estimate sleep stages at home rather than measuring brain activity in a sleep laboratory. And the new abstract does not establish that changing a schedule will prevent disease. Columbia University sleep researcher Marie-Pierre St-Onge, who was not involved in the analysis, says evidence for an independent causal effect of regularity remains insufficient.newsroom

A practical starting point

A consistent bedtime and wake time may help people obtain sufficient sleep, but regularity is not a substitute for duration. The American Academy of Sleep Medicine and Sleep Research Society recommend at least seven hours per night for healthy adults aged 18 to 60, and advise people who suspect a sleep disorder to consult a doctor.newsroom +1