If you want a healthy heart, there are few better ways to start than getting an early night's sleep – but not too early.
Regularly falling asleep between 10 pm and 11 pm is linked to a lower risk of developing heart disease, according to a new study published in the European Heart Journal – Digital Health.
The study found that, compared to falling asleep from 10 pm to 11 pm, people who fell asleep at midnight or later had a 25 percent higher risk of cardiovascular disease. The risk was 12 percent greater for those who dozed off between 11 pm and midnight. Interestingly, there was also a raised risk for those that hit the hay too early, with a 24 percent increased risk for people asleep by 10 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. 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. study author from the University of Exeter, said in a statement.
"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," Dr Plans explained.
The new study looked at 7 days' worth of data on sleep onset and waking up time from over 88,000 people who participated in the UK Biobank project, collected via an accelerometer worn on the wrist. Participants also filled out a questionnaire asking about their demographics, lifestyle, wider health, and physical assessments. They were then followed up years later for a new diagnosis of cardiovascular disease, including heart attacks, heart failure, chronic ischaemic heart disease, stroke, and transient ischaemic attack. After accounting for other factors, such as smoking status, body mass index, and socioeconomic status, the team then analyzed how the sleep onset time was linked to the risk of cardiovascular disease.
As Dr Plans explained, the study did not look to explain the potential cause behind the apparent link. However, a mountain of previous studies has highlighted the link between heart health and sleep quality. Scientists don’t completely understand this relationship, but it’s likely to do with sleep’s influence on biological processes like glucose metabolism, blood pressure, and inflammations
One thing that became apparent in this new study was how the link between sleep onset and cardiovascular disease was more obvious among women compared to men. The reason for this isn’t known, but the researchers suspect it might have something to do with hormones.
“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,” adds Dr Plans.