New research suggests that going to sleep between 10pm and 11pm lowers the risks of heart disease.
Compared to sleep between 10pm to 10:59pm, there was a 12% greater risk of heart disease for 11pm to 11:59pm and a 24% increase risk when going to sleep before 10pm.
Further analysis by sex suggested the association with increased cardiovascular risk was stronger in women, with only sleep onset before 10pm remaining significant for men.
How was the research carried out?
The UK Biobank study involved 88,026 adults recruited between 2006 and 2010.
The average age was 61, with a range between 43 to 79 years and 58% were women.
Data on sleep onset and waking up time over seven days was collected from 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 - defined as a heart attack, heart failure, chronic ischaemic heart disease, stroke, and transient ischaemic attack.
The study was published in the European Heart Journal, Digital Health, a journal of the European Society of Cardiology (ESC).
What did the study find?
During an average follow-up of 5.7 years, 3,172 participants (3.6%) developed cardiovascular disease.
The incidence was highest in those with sleep times at midnight or later and lowest with those from 10pm to 10:59pm, the paper found.
“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,” study author Dr David Plans, of the University of Exeter, said.
Dr Plans added: “The riskiest time was after midnight, potentially because it may reduce the likelihood of seeing morning light, which resets the body clock.”
Why was there a stronger link in women?
The reasons for the stronger association between sleep onset and cardiovascular disease in women is unclear, according to Dr Plans.
“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 said.
What has been said?
Dr Plans highlights that the “results suggest that early or late bedtimes may be more likely to disrupt the body clock, with adverse consequences for cardiovascular health.”
“Sleep timing has emerged as a potential cardiac risk factor – independent of other risk factors and sleep characteristics,” he added.
However, Regina Giblin, senior cardiac nurse at the British Heart Foundation, points out “it’s important to remember that this study can only show an association and can’t prove cause and effect.”
Ms Giblin said: “More research is needed into sleep timing and duration as a risk factor for heart and circulatory diseases.
“Getting enough sleep is important for our general wellbeing as well as our heart and circulatory health, and most adults should aim for seven to nine hours of sleep per night.”