# Harvard study of 10,000 Americans links irregular sleep timing to 20–23% higher heart and stroke risk

- Published: 2026-11-07 19:37 UTC
- Section: Life & Health › Medicine
- Tags: irregular sleep and heart risk, sleep timing, sleep regularity, heart failure risk, stroke risk, sleep trackers, REM sleep cycles, atrial arrhythmia
- URL: https://realtech.media/news/rt-5a35382565180d3baf61911f_harvard_study_of/

**In a US study with sleep trackers, night-to-night changes in sleep timing over about six months were associated with a higher risk of heart attack, stroke and heart failure.**

![Harvard study of 10,000 Americans links irregular sleep timing to 20–23% higher heart and stroke risk](https://realtech.media/media/2026/11/b03d1338ddf88b98.avif)
*mirror.co.uk*

Researchers led by Dr Nguyen Minh Tuan Viet of Harvard Medical School tracked the sleep of 10,000 Americans with wearable devices for six months, mirror.co.uk reports. The dataset covers more than one million nights, and both duration and quality of sleep were analysed. Participants were then followed for four years to record heart problems. The results are being presented at the American Heart Association's Scientific Sessions 2026 in Chicago. [1]

## Irregular sleep timing and heart risk

Changes in sleep timing from night to night over about six months were linked to a 20–23% higher risk of heart attack, stroke and heart failure. [1] Each additional half hour of night-to-night variation in sleep length was associated with a 29% higher risk of a disease of the heart muscle, which leaves the heart unable to pump enough blood, and a 20% higher risk of heart failure. [1]

Viet said sleep irregularity often comes from weekends, when people go to bed later on Friday, or from shift work. In his words, sleep quality is sometimes outside a person's control, while consistent bedtimes and a fixed wake-up time are something some people can control.

## Sleep cycles and REM sleep

The study also measured time spent in light, deep and rapid eye movement (REM) sleep. REM sleep consists of periods of rapid brain activity when people dream, and it makes up about a quarter of the night. A "sleep cycle" was defined as the interval from the end of one REM period to the end of the next, including the light and deep stages in between. [1]

A greater number of complete sleep cycles per night was associated with a 28% lower risk of atrial arrhythmia, a common type of irregular heartbeat. An unusually long sleep cycle was linked to a 55% higher risk of heart attack or stroke. [1] Earlier research has shown that late bedtimes, alcohol close to bedtime and certain medications can disrupt REM sleep.

Viet, who also works as a neuroscientist at Boston Children's Hospital, said a regular schedule, with consistent bedtimes, wake times and sleep duration, is a practical step that may help protect the heart and blood vessels.

The article notes that the average British adult sleeps 6 to 6.4 hours per night, below the recommended 7 to 9 hours. It also refers to a separate study of 41,000 adults over seven years, presented at the European Society of Cardiology congress in Munich in August. According to its authors, a weekend lie-in of 1 hour 27 minutes was associated with a 9% lower likelihood of high blood pressure.

## Sources

1. [mirror.co.uk](https://www.mirror.co.uk/news/health/sleep-heart-lie-regular-bedtime-37833329)
2. [medonet.pl](https://www.medonet.pl/narodowy-test-zdrowia-polakow/zyj-zdrowiej/lubisz-pospac-w-weekend-uczeni-z-harvardu-rosnie-ryzyko-udaru/bpy3hlr)

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Source: RealTech, realtech.media — https://realtech.media/news/rt-5a35382565180d3baf61911f_harvard_study_of/