Going to bed between 10 and 11 PM may be good for your heart — especially if you’re a woman.

It’s been shown time and time again that not getting enough sleep is bad for your heart (and bad for you in general, for a number of reasons). But not all sleep is equal, and not all bedtimes are equal. In a new study, researchers analyzed data from over 88,000 individuals in the UK Biobank, collecting data on their sleep and waking up time using a monitoring bracelet. Researchers then followed up four years later, looking for any cardiovascular diseases (such as heart attack, heart failure, chronic ischaemic heart disease, stroke, and transient ischaemic attack). Over 3,000 people developed cardiovascular disease over the period of the study.

The ideal period for going to sleep (the one that was correlated with the lowest risk of heart disease) was 10-11 PM. Many of the people who developed a disease went to sleep after 11 PM — the risk was 12% greater for those who went to sleep between 11:00 and 11:59 PM, 25% disease higher for those going to bed after midnight, and remarkably, 24% higher for those who went to sleep before 10 PM.

While this is just relative risk, and the total risk was still relatively low (just 3.6% of participants developed a disease), the differences are significant, especially because the data was acquired directly (as opposed to self-reporting, which is often used in this type of study but can be inaccurate).

Still, the study only establishes a correlation, which does not necessarily imply causation — so in other words, no cause-effect link was yet demonstrated. However, researchers stress that the link persisted after adjustments were made for sleep duration and sleep irregularity.

“The body has a 24-hour internal clock, called circadian rhythm, that helps regulate physical and mental functioning,” said study author Dr. David Plans of the University of Exeter, UK. “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.”

However, there were important gender differences. The association with increased cardiovascular risk was stronger in women — only sleeping before 10:00 PM remained as significant for men. Researchers aren’t exactly sure why this seems to be the case, but they suggest that sleep timing may be a risk for everyone, not just for women.

“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.”

Based on these findings, researchers suggest to try and go to sleep sometime between 10 and 11 PM — or at least before midnight. The more you delay, the more pressure you are likely putting on your body.

“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,” Plans added.

Going to bed before midnight can be pretty challenging, especially in our modern, fast-paced world. However, here are a few science-based things you can do to ease your way into a good night’s sleep:

• Turn off all artificial lights — yes, this includes your smartphone, laptop, TV, whatever. Because the natural production of melatonin (which is required for sleep) can be suppresed by light, looking into a screen may prevent the body from feeling sleepy.
• Staying away from caffeine hours before bedtime — give enough time for the caffeine to exit the body.
• Stay physically active — there is solid evidence that physical activity can help improve your sleep quality. Intense physical activity less than two hours before bedtime should be avoided, but otherwise, exercising really helps.
• Meditation and relaxation techniques can also help — although more research is needed, there is evidence that things like breathing exercises, meditation, and relaxation methods can help reduce your stress levels and help you fall asleep faster.

Journal Reference: Nikbakhtian S, Reed AB, Obika BD, 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.