“The body has a 24-hour internal clock, called circadian rhythm, that helps regulate physical and mental functioning,” said researcher Dr. David Plans. “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.”
Not too late and not too early
For the study, the researchers analyzed data from more than 88,000 individuals enrolled in the U.K. Biobank between 2006 and 2010. Over the course of seven days, the researchers tracked the participants’ sleep habits with a wrist monitor. Later, the team conducted comprehensive medical exams to determine the participants’ health status.
Ultimately, the researchers learned that participants with bedtimes that were later than midnight and earlier than 10:00 p.m. had the highest risks of developing heart disease. However, those who were able to fall asleep between 10:00 p.m. and 11:00 p.m. were likely to have the best heart health outcomes.
“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,” said Dr. Plans. “The riskiest time was after midnight, potentially because it may reduce the likelihood of seeing morning light, which resets the body clock.”
The highest heart health risks were for night owls and early sleepers. Participants who went to bed past midnight and those who went to bed before 10:00 p.m. had a 25% and 24% increased risk of heart disease, respectively. Comparatively, those who fell asleep between 11:00 p.m. and midnight had a 12% higher risk of heart disease.
Moving forward, the team hopes to do more work in this area to better understand how consumers’ sleep habits impact their long-term heart health.
“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,” said Dr. Plans. “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.”