Sleep

What's the best time to fall asleep? Researchers have found the 'sweet spot'

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  • The 'perfect' bedtime for heart health has been underresearched, according to a new study.
  • Researchers suggest that falling asleep around a particular time may have benefits for heart health.
  • The study has some limitations, and additional, larger studies are needed.

The demands of modern-day living and work stress have led to many of us functioning on little sleep and hardly giving any thought to our sleep patterns. With millions of people globally sleep-deprived, health experts have warned about the impact on our health. 

Ongoing, insufficient sleep is one of the contributing factors to poor heart health and has been linked to heart attack, high blood pressure (hypertension), and even stroke.

While the association between sleep duration and cardiovascular disease has been known for some time, the nitty-gritty of sleep timing and heart health hasn’t been much explored. 

A new study, however, suggests that there’s an optimal time to drop off when it comes to ensuring a healthy cardiovascular system: between 22:00 and 23:00.

An earlier or later bedtime may lead to our bodies missing cues that help reset our 24-hour body clock each day, the researchers say.

Body’s 24-hour internal clock

"The body has a 24-hour internal clock, called circadian rhythm, that helps regulate physical and mental functioning," co-author David Plans, head of research at Huma Therapeutics and senior lecturer at the University of Exeter, said in a news release about the study. 

While the study can’t prove that early or late bedtimes contribute to the development of cardiovascular disease, their findings suggest that they may be “more likely to disrupt the body clock, with adverse consequences for cardiovascular health".

For example, one possibility is that early or late bedtimes may result in individuals missing important cues, such as morning light, which help to reset the body’s clock each day.

If the body clock is not reset properly over a long time, “that misalignment of behaviours and the circadian clock increases inflammation and can impair glucose regulation, both of which can increase risk of cardiovascular disease”, he said.

The riskiest time to fall asleep is after midnight, they found.

Over 3 000 developed cardiovascular disease

For the study, the researchers analysed wrist-worn accelerometer data from 88 026 participants in the UK Biobank study recruited between 2006 and 2010. 

They then compared participants’ sleep timing over a seven-day period with later health outcomes. Participants were asked to complete a number of assessments, including demographic, lifestyle, and physical assessments, as well as questionnaires. 

They were followed up after almost six years. Plans and colleagues reported that 3 172 of the 88 026 participants developed cardiovascular disease during this time – none of whom had the condition, or a sleep disorder, when they were recruited for the study.

Results

The researchers determined the following in the participants who developed cardiovascular disease:

  • 1 371 fell asleep after midnight  
  • 1 196 fell asleep in the hour between 11 pm and midnight 
  • 473 fell asleep in the hour between 10 and 11 pm
  • 132 dozed off before 10 pm

Compared to nodding off between 22:00–23:00, doing so after midnight or before 22:00 was associated with around a 25% increase in the risk of cardiovascular disease. This risk dropped to 12% for participants who fell asleep between 23:00 and 00:00.

Various details were taken into account, including participants’ age, sex, smoking status, socioeconomic status, duration of sleep, diabetes, blood pressure, but the trend remained, the authors said.

Risk stronger in women than men

The findings also appeared to be stronger in women than men, but the reasons for this remain unclear, said Plans.

“It may be that there is a sex difference in how the endocrine system responds to a disruption in circadian rhythm,” he explained. “Alternatively, the older age of study participants could be a confounding factor since cardiovascular risk in women increases post-menopause – meaning there may be no difference in the strength of the association between women and men.”

Some study limitations

The study had some limitations, including age and ethnicity (participants were predominantly wealthier white people aged 43 to 79 years old), which means the findings may not necessarily be the same for other demographics. Moreover, the researchers didn’t closely assess the quality of sleep, and focused instead on length and timing.

Commenting on this, Plans said additional research, with larger numbers of participants, is needed to examine the findings, considering this area of sleep and heart health is under-researched.

He concluded: “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.”

Their findings were reported in European Heart Journal – Digital Health.

Struggling to nod off?

If you frequently find yourself lying awake in bed, unable to drift off, here are some tips that might help: 

  • Drink a warm cup of milk or chamomile tea before bedtime – it may relax the brain and body.
  • Reserve your bed for sleep and sex, not work or TV, say Harvard Health experts.
  • Eat a light dinner.
  • Limit your alcohol and caffeine intake before bed as it can affect your quality of sleep.
  • Practice meditation and mindfulness (there are plenty of apps available) – as a relaxation technique, it may help prepare your mind for drifting off to sleep.

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READ | Why do I feel like I’m slipping or falling as I'm about to fall asleep?

READ | Listening to music close to bedtime may disrupt sleep - here's why

READ | The recovery of your brain depends greatly on sleep, and it cannot be replaced by rest

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