It is widely recognised that insufficient sleep increases heart attack risk, even if the reasons aren’t fully clear.
Now a new study has put some hard numbers around that risk – and also found that getting too much sleep can be just as big a problem.
Simply being healthy doesn’t help if you don’t sleep right, according to the findings reported in in the Journal of the American College of Cardiology, but for those at high genetic risk for heart attacks, sleeping between six and nine hours nightly can offset risk.
The research was led by Celine Vetter from the University of Colorado Boulder, US, and included researchers from the Massachusetts General Hospital, US, and the University of Manchester, UK.
They analysed the genetic information, self-reported sleep habits and medical records of 461,000 UK Biobank participants aged 40 to 69 who had never had a heart attack, then followed them for seven years.
After taking into account 30 other factors – including body composition, physical activity, socioeconomic status and mental health – they found that sleep duration, in and of itself, influenced heart attack risk independently of these other factors.
Compared to those who slept six-to-nine hours per night, those who slept fewer than six hours were 20% more likely to have a heart attack during the study period. Those who slept more than nine hours were 34% more likely.
When the researchers looked only at people with a genetic predisposition to heart disease, they found that sleeping between six and nine hours nightly cut their risk of having a heart attack by 18%.
“This provides some of the strongest proof yet that sleep duration is a key factor when it comes to heart health, and this holds true for everyone,” says Vetter.
The study also suggests that the risks increases as you get further outside the six-to-nine-hour range.
People who slept five hours per night had a 52% higher risk of heart attack than those who slept seven to eight hours, for example, while those who slept 10 hours nightly were twice as likely to have one.
Using a Mendelian randomisation, which incorporates genetic information into traditional epidemiologic methods, the researchers then looked at participant’s genetic profiles.
They saw similar patterns emerge and found that genetically influenced short sleep duration was a risk factor for heart attack.
“This gives us even more confidence that there is a causal relationship here – that it is sleep duration, not something else, influencing heart health,” Vetter says.
Nick Carne is editor of Cosmos digital and editorial manager for The Royal Institution of Australia.
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