Previous research has investigated a link between sleep duration and cardiovascular disease, but this is one of the first to find a relationship between sleep timing and heart disease.
Study author Dr. David Plans explained, “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.”
For the study, data from 88,026 individuals in the UK biobank were analyzed. The average age was 61 years, and 58% were women. Information on sleep onset and waking up time were collected over seven days from participants using a wrist accelerometer.
All participants were required to complete lifestyle, demographic, health, and physical assessments in questionnaires. They were followed up for an average of 5.7 years for any new diagnosis of cardiovascular disease, which was defined as heart failure, heart attack, chronic ischaemic heart disease, stroke, and transient ischaemic attack.
The association between cardiovascular events and sleep onset was adjusted for age, sex, sleep duration, sleep irregularity, smoking status, body mass index, diabetes, blood pressure, blood cholesterol, and socioeconomic status.
During the follow-up, 3,172 participants developed cardiovascular disease. Researchers found, the 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 PM.
Sleep Timing
Researchers believe that the study indicates that the optimum time to go to sleep is at a specific point in the body’s 24-hour cycle, and deviations could be hazardous to health. The riskiest time was after midnight because it may reduce the likelihood of the eyes seeing the morning sun, which can help reset the body clock.
When the information was analyzed by sex, the association with increased cardiovascular risk was stronger in women. Researchers believe it may be because there is a sex difference in how the endocrine system responds to a disruption in circadian rhythm.
The research team is hopeful that these findings will be confirmed in other studies so that sleep timing and basic sleep hygiene could be a low-cost way to target the risk of heart disease.
Getting a good quality night’s sleep has previously been linked to overall better physical health and mental health. For better quality sleep, try going to bed around the same time each night, turning off any electronic devices at least an hour before bedtime, and reducing caffeine intake a few hours before bedtime.