Failure 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, the most comprehensive study of his sort of.
Previous studies have focused on the link between sleep duration and health outcomes, with people advised to keep an eye on between seven and nine hours a night.
That advice still stands. But researchers are increasingly focusing on sleep patterns, and in particular the impact of irregular sleep – defined as variations in the time a person goes to sleep and wakes up.
The new study found that irregular sleep — going to bed and waking up at different times each day — was “strongly associated” with an increased risk of serious adverse cardiovascular events. Even getting eight hours of sleep was insufficient to offset the harmful effects of consistently varying bedtimes and wake-up times, experts said.
The research, published in the Journal of Epidemiology and Community Health, involved 72,269 people aged 40 to 79 from the UK Biobank study. It didn’t establish exactly how close you should get to the same bed and rise time – just that the further you are, the greater the risk of harm.
Lead author Jean-Philippe Chaput, from the University of Ottawa, said: “We should aim to wake up and go to bed within 30 minutes of the same time every night and every 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.
“Beyond an hour’s difference means irregular sleep every night and every morning. This can have negative health impacts. The closer you are to zero variation, the better.
“No one is perfect for an entire year, and if you don’t have a regular sleep pattern for one or two days a week, it’s not going to kill you. But if you repeatedly sleep irregularly five or six days a week, then it becomes chronic, and that’s a problem.”
Chaput said waking up at the same time every day is more important than going to bed at the same time. “Waking up at different times every morning really messes with your internal clock, and that can have adverse health effects,” he said.
“If you need to catch up on the sleep you missed during the week at the weekend, it’s better to go to bed earlier than to lie down – you should still try to wake up at the same time, even on Saturdays and Sundays.”
In the study, participants wore an activity tracker for seven days to record their sleep, with experts then calculating a sleep regularity index (SRI) score for each person.
The score captured the day-to-day variability in bedtime, wake time, sleep duration and waking during the night, with people giving a score ranging from 0 (very irregular) to 100 (perfectly regular sleep-wake pattern) .
Participants were placed into either an irregular sleep group (SRI score less than 71.6), moderate irregular sleep group (SRI between 71.6 and 87.3), or regular sleep group (SRI score greater than 87.3). People were then followed up for eight years.
Even after taking into account factors that could affect the results, irregular sleepers were 26% more likely to have a stroke, heart failure or heart attack than those with regular sleep, the study found. Moderately irregular sleepers were 8% more likely to do so.
Researchers found the SRI score was a continuous measure, with people’s risk of heart attack and stroke increasing the more irregular their sleep patterns were.
The recommended amount of sleep for 18- to 64-year-olds is seven to nine hours a night, and seven to eight hours for those 65 and older.
The study found a greater proportion of regular sleepers (61%) met the recommended sleep quota than irregular sleepers (48%). But it made no difference to heart health for irregular sleepers, who had the same increased risk of stroke and heart attack even if they got enough sleep.
In contrast, moderately irregular sleepers saw their risks drop when they got adequate sleep.
This was an observational study, and as such could not establish cause and effect, and the researchers acknowledged several limitations to their findings.
But they concluded that the findings suggest that irregular sleep is strongly associated with a risk of major adverse cardiovascular events in adults, regardless of whether the recommended sleep quotas were met or not.
“More importantly, our results suggest that sleep regularity may be more relevant than adequate sleep duration in modulating major adverse cardiovascular event risk.”
