A research team in the UK has identified the optimal time window for sleep that maximises heart health, finding that deviating from this sleep schedule can greatly affect it.
The study, which is published in the European Heart Journal – Digital Health, a journal of the European Society of Cardiology (ESG), has found that going to sleep between 10:00 pm and 11:00 pm can enhance heart health. This timeframe demonstrated an association with a lower risk of developing heart disease compared to earlier or later bedtimes.
Dr David Plans, the author of the study from the University of Exeter, UK, 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.”
The importance of sleep
An array of previous studies have investigated the relationship between sleep duration and cardiovascular disease; however, the impacts of sleep timing and heart disease remains considerably unexplored. This novel study analysed the association between objectively measured, instead of self-reported, sleep onset in a large sample of adults, determining how it influences heart health.
To conduct their research, the team examined 88,026 individuals in the UK Biobank, recruited between 2006 and 2010. The age of the individuals ranged from 43 to 79 years, with the average age being 61 and 58% of the participants being women. The researchers utilised wrist-worn accelerometers to collate data on sleep onset and waking up times from the individuals over seven days.
Additionally, the participants completed demographic, lifestyle, health and physical assessments and questionnaires and followed up for a new diagnosis of cardiovascular disease, which was defined as a heart attack, heart failure, stroke, chronic ischaemic heart disease, and transient ischaemic attack.
Optimising heart health
Throughout the average follow-up period of 5.7 years, 3,172 of the participants – 3.6% – developed cardiovascular disease, with the incidence being highest for those whose sleep times were midnight or later and lowest in those between 10:00 pm to 10:59 pm.
Next, the researchers investigated the effects of sleep onset on heart health after adjusting for age, sex, sleep duration, sleep irregularity (defined as various 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.
In comparison to people with sleep onset between 10:00 pm to 10:59 pm, people who went to sleep at midnight or later displayed a 25% higher risk of cardiovascular disease, those between 11:00 pm and 11:59 pm had a 12% greater risk, and individuals who went to sleep earlier than 10:00 pm had a 25% increased risk. Subsequently, the team performed an additional analysis based on sex, finding that the association with cardiovascular disease risk was higher in women, with only sleep onset before 10:00 pm being higher 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.
“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.
“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 the risk of heart disease.”