What time you go to sleep is linked to your risk for heart disease, according to a study published in European Heart Journal - Digital Health.
"The body has a 24-hour internal clock, called circadian rhythm, that helps regulate physical and mental functioning,” said study author Dr David Plans. “While we cannot conclude causation from our study, the results suggest that early or late bedtimes may be more likely to disrupt the body clock, with adverse consequences for cardiovascular health."
The study looked at 88,026 participants in the UK Biobank study, recruited between 2006 and 2010. The average age of the people included was 61 years, and 58% were women. Data on sleep onset and waking time were collected from accelerometer readings over 7 days, along with information about lifestyle, health, and physical fitness. They were then cross referenced with any new diagnosis of cardiovascular disease, including heart attack, heart failure, stroke, chronic ischaemic heart disease, and transient ischaemic attack.
Over an average follow-up of 5.7 years, 3172 participants (3.6%) developed cardiovascular disease. Incidence was highest amongst those who had a sleep onset time at midnight or later, and lowest in those who went to sleep between 10-11 pm.
"Our study indicates that the optimum time to go to sleep is at a specific point in the body’s 24-hour cycle, and deviations may be detrimental to health," said Dr Plans. "The riskiest time was after midnight, potentially because it may reduce the likelihood of seeing morning light, which resets the body clock."
Those who slept from midnight or later had a 25% higher risk for developing cardiovascular disease than those who slept between 10-11 pm, while those who slept before 10 pm had a 24% higher risk. The association between sleep and heart health was stronger in women, although the reason for this remains unclear.
"It may be that there is a sex difference in how the endocrine system responds to a disruption in circadian rhythm. Alternatively, the older age of study participants could be a confounding factor, since women’s cardiovascular risk increases post-menopause – meaning there may be no difference in the strength of the association between women and men," Dr Plans said.