Going to sleep between 10pm and 11pm could result in a lower risk of developing heart disease, new research has found.
The study found compared to falling asleep between 10pm and 10.59pm there was a 12% greater risk for 11pm to 11.59 pm, and a 24% increased risk for falling asleep before 10pm.
Meanwhile, there was a 25% higher risk of cardiovascular disease associated with falling asleep at midnight or later.
Study author Dr David Plans, of the University of Exeter, said: “The body has a 24-hour internal clock, called circadian rhythm, that helps regulate physical and mental functioning.
“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.”
Further analysis by sex found the increased cardiovascular risk was stronger in women.
The study included 88,026 people in the UK Biobank study, recruited between 2006 and 2010. The average age was 61 years, with participants aged between 43 and 79 years old, with 58% women.
Researchers collected data on sleep onset and waking up time over seven days using a device worn on the wrist.
Participants completed demographic, lifestyle, health, and physical assessments and questionnaires.
They were then followed up for a new diagnosis of cardiovascular disease, which was defined as a heart attack, heart failure, chronic ischaemic heart disease, stroke, and transient ischaemic attack.
During an average follow-up of 5.7 years, 3,172 participants (3.6%) developed cardiovascular disease, according to the study published in European Heart Journal – Digital Health, a journal of the European Society of Cardiology (ESC).
According to the paper, this was highest in those with sleep times at midnight or later and lowest in those with sleep onset from 10pm to 10.59 pm.
Dr Plans said: “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.
“The riskiest time was after midnight, potentially because it may reduce the likelihood of seeing morning light, which resets the body clock.”
He added that the reasons for the observed stronger association between sleep onset and cardiovascular disease in women is unclear.
Dr Plan said: “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.”
He concluded: “While the findings do not show causality, sleep timing has emerged as a potential cardiac risk factor – independent of other risk factors and sleep characteristics.”
Regina Giblin, senior cardiac nurse at the British Heart Foundation, said while more research is needed, most adults should aim for seven to nine hours of sleep per night: “This large study suggests that going to sleep between 10 and 11pm could be the sweet spot for most people to keep their heart healthy long-term.
“However, it’s important to remember that this study can only show an association and can’t prove cause and effect.”