Watching your favourite TV shows till late at night might relax you, but going to bed late every night can increase your risk of heart disease. In fact, a new study shows there is a sweet spot for falling asleep: between 10 to 11 p.m.
The link between sleep duration and cardiovascular disease, and the relationship between sleep timing and heart disease is under-explored, researchers from the United Kingdom concludes.
Their study was published this week in the European Heart Journal of the European Society of Cardiology.
“The body has a 24-hour internal clock, called circadian rhythm, that helps regulate physical and mental functioning,” explains study author Dr David Plans.
He adds that the results suggest that early or late bedtimes may be more likely to disrupt the body clock, with negative consequences to your heart.
The study conducted by the University of Exeter, examined the association between measured, rather than self-reported, sleep onset in over 88 000 adults.
Let’s break it down
Biobank recruited 88 026 people in the UK between 2006 and 2010.
The average age was 61 years and 58% were women. Data on sleep onset and waking up time were collected over seven days using a wrist-worn accelerometer.
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 and stroke.
During an average follow-up of 5.7 years, 3 172 participants (3.6%) developed cardiovascular disease.
Incidence was highest in those with sleep times at midnight or later and lowest in those with sleep onset from 10:00 to 10:59 p.m.
The researchers analysed the association between sleep onset and cardiovascular events after adjusting for age, sex, sleep duration, sleep irregularity, self-reported chronotype, smoking status, body mass index, diabetes, blood pressure, blood cholesterol and socioeconomic status.
Compared to sleep onset from 10:00 to 10:59 p.m., there was a 25% higher risk of heart disease with a sleep onset at midnight or later, a 12% greater risk for 11:00 to 11:59 p.m., and a 24% raised risk for falling asleep before 10:00 p.m.
In a further analysis by gender, the association with increased cardiovascular risk was stronger in women, with only sleep onset before 10:00 p.m. remaining significant for men.
“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 David Plans, senior lecturer in organisational neuroscience (SITE) at the University of Exeter
Plans also notes that the reasons for the observed stronger association between sleep onset and cardiovascular disease in women is 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.”
He concludes: “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.”
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