The optimal time to fall asleep is between 10 pm and 11 pm, according to a new study from the United Kingdom, published in the European Heart Journal – Digital Health. The study further suggests that sleeping between this time is associated with a lower risk of heart disease when compared to going to sleep earlier or later.

For the study, the researchers analysed a subsample of 88,026 persons, mean age 61 years, from the UK Biobank enrolled between 2006 and 2010. Women comprised nearly 60% of the study population. Sleep onset and waking up time were measured over a week with an accelerometer device worn on the wrist. The participants were followed up for 5.7 years (mean) to identify any association between the timing of sleep onset and the incidence of new cardiovascular events.

Data analysis revealed that 3172 participants (3.6%) developed CVD during the follow up period. Of these 3172 participants, 1371 (43%) slept after midnight; 1196 (38%) had sleep onset time between 11 pm and 11.59 pm and 132 (4.2%) slept before 10 pm. A sleep onset time from 10 pm to 10:59 pm was associated with the lowest incidence of CVD, while the incidence was highest in individuals who went to sleep earlier or later than this time. Those who slept after midnight had higher likelihood of being current smokers and having a history of diabetes or hypertension vs those with sleep onset time from 11 pm-11.59 pm, 10 pm to 10.59 pm and before 10 pm

Compared to sleep onset time of 10 pm to 10:59 pm, the risk of CVD was 25% higher for those falling asleep at midnight or later; for those with sleep onset time between 11 pm and 11:59 pm, the risk increased by 12%, and the risk of CVD was increased 24% for those who sleep before 10 pm. The association with increased CVD risk was found to be stronger in women, whereas only sleep onset before 10pm was significant for men. This association persisted even after adjustment for the traditional risk factors for heart disease such as hypertension, diabetes, overweight and obesity and smoking.

While a cause-and-effect association could not be ascertained, this study has shown a clear link between time of sleep onset and risk of heart disease, particularly for women and proposes timing of sleep as a new modifiable risk factor for heart disease. Those who slept after midnight were at the greatest risk as were those who slept early. As study author Dr David Plans of the University of Exeter, UK said, “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.”

Reference

1. Nikbakhtian S, et al. Accelerometer-derived sleep onset timing and cardiovascular disease incidence: a UK Biobank cohort study. Eur Heart J Digit Health. 2021. doi:10.1093/ehjdh/ztab088