Failing to stick to a regular bedtime and wake-up time increases the risk of stroke, heart attack and heart failure by 26%, even for those who get a full night's sleep, according to the most comprehensive study of its kind. The research, published in the Journal of Epidemiology and Community Health, involved 72,269 people aged 40 to 79 from the UK Biobank study.
Experts said irregular sleep – defined as variations in the time a person goes to sleep and wakes up – was “strongly associated” with a higher risk of major adverse cardiovascular events. Even getting eight hours of sleep was insufficient to offset the harmful effects of consistently varying bed and wake-up times.
Lead author Jean-Philippe Chaput of the University of Ottawa said: “We should aim to wake up and go to sleep within 30 minutes of the same time each night and each morning, including weekends. Within an hour of the same time is good but less good than 30 minutes, and even better is to have zero variation.” He added that waking up at the same time each day was more important than going to bed at the same time.
In the study, participants wore an activity tracker for seven days to record their sleep. Experts calculated a sleep regularity index (SRI) score from 0 (very irregular) to 100 (perfectly regular). Participants were grouped into irregular (SRI less than 71.6), moderately irregular (SRI 71.6–87.3), or regular sleepers (SRI over 87.3) and followed for eight years.
Irregular sleepers were 26% more likely to suffer a stroke, heart failure or heart attack than regular sleepers, while moderately irregular sleepers were 8% more likely. The risk increased the more irregular the pattern. The study found no difference in risk for irregular sleepers even if they met the recommended seven to nine hours of sleep.
The researchers acknowledged limitations as an observational study but concluded that irregular sleep was strongly associated with cardiovascular risk in adults, irrespective of sleep duration.
