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'Early or late bedtimes may be more likely to disrupt the body clock'

Going to sleep at 10pm linked to lowered risk of heart disease

A new study has revealed the optimum time for going to sleep to avoid developing heart disease.

A bedtime of between 10 and 11pm carries a lower risk of developing heart disease compared to earlier or later bedtimes, according to the study, co-authored by Dr David Plans, a Senior Lecturer at the Initiative in Digital Economy at Exeter (INDEX), part of the University of Exeter Business School.

“The body has a 24-hour internal clock, called circadian rhythm, that helps regulate physical and mental functioning,” said Dr Plans, who is also Head of Research and Scientific Dissemination at Huma. “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 used data from 88,026 participants of the UK Biobank, and collected data on sleep onset and waking up times over seven days using a wrist-worn accelerometer.

Participants completed demographic, lifestyle, health and physical assessments and questionnaires which were followed up with a new diagnosis for cardiovascular disease, 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.

This was highest in those with sleep times at midnight or later, and lowest in those who went to sleep from 10pm to 10.59pm.

The researchers analysed the association between sleep onset and cardiovascular events after adjusting for age, sex, sleep duration, sleep irregularity (defined as varied times of going to sleep and waking up), self-reported chronotype (early bird or night owl), smoking status, body mass index, diabetes, blood pressure, blood cholesterol and socioeconomic status.

Those who went to bed at midnight or later had a 25% higher risk of cardiovascular disease compared with those who went to bed at the optimum time range of between 10pm and 10.59pm.

Those whose bedtime was between 11pm and 11.59pm had a 12% raised risk, and those who fell asleep before 10pm had a 24% raised risk. 

In a further analysis by sex, the association with increased cardiovascular risk was stronger in women, with only sleep onset before 10pm remaining significant for men.

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.”

Dr Plans noted that the reasons for the observed stronger association between sleep onset and cardiovascular disease in women is unclear.

He 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. If our findings are confirmed in other studies, sleep timing and basic sleep hygiene could be a low-cost public health target for lowering risk of heart disease.”

Date: 9 November 2021

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