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Researchers at the University of Ottawa in Canada found that inconsistent bedtimes and wake-up times raise the risk of stroke, heart attack, and heart failure by 26 percent—even for people who get enough hours of sleep.
Previous studies focused on sleep duration and recommended seven to nine hours per night. That advice still stands. But researchers are now paying more attention to sleep patterns, especially irregular sleep, which means variation in when someone falls asleep and wakes up.
What Did the New Study Reveal?
The latest findings show that even eight hours of sleep may not offset the harm from inconsistent bedtimes and wake-up times.
The large-scale study tracked 72,269 people aged 40 to 79 who continuously wore sleep trackers to monitor their sleep patterns. Researchers then calculated a Sleep Regularity Index (SRI) for each participant.
The index reflected daily variation in bedtime, wake-up time, total sleep duration, and nighttime awakenings. Participants received scores ranging from 0 (very irregular sleep and wake patterns) to 100 (perfectly regular sleep and wake patterns).
Volunteers were grouped by sleep regularity: irregular sleep (SRI below 71.6), moderately irregular sleep (SRI 71.6–87.3), and regular sleep (SRI above 87.3). The team followed them for eight years.
After adjusting for other factors, people with irregular sleep were 26 percent more likely to have a stroke, heart failure, or heart attack than those with regular schedules. People with moderately irregular sleep had an 8 percent higher risk, The Guardian reported.
The study found that 61 percent of people with regular sleep met the recommended sleep duration, compared with 48 percent of those with irregular sleep.
Among people with moderately irregular sleep, the risk of developing cardiovascular disease fell if they were getting adequate rest. Recommended sleep duration for adults aged 18 to 64 is 7–9 hours; for those 65 and older it is 7–8 hours.
Expert Recommendations
The study’s lead author, Jean-Philippe Chaput, said, “We should aim to wake up and go to bed within 30 minutes of the same time, including on weekends. A one-hour variation is less ideal, and zero variation is best.”
Chaput said missing a regular schedule one or two days a week won’t be harmful, but consistently irregular sleep becomes a chronic problem.
It’s particularly important to wake up at the same time each day. Irregular wake-up times disrupt the body’s internal clock and can harm health.
Chaput advised, “If you need to catch up on lost sleep over the weekend, it’s better to go to bed earlier than to sleep in. Try to wake up at the same time even on Saturday and Sunday.”
The results were published in the Journal of Epidemiology and Community Health.
