Scientists find the best bedtime for heart health

To improve your heart health, you may need to cultivate a rather counterintuitive habit: Start watching The Daily Show online the day after it airs on television. The reason why is to do with when you should hit the hay for the night.

Researchers in the U.K. have discovered that people who usually fall asleep between 10 p.m. and 11 p.m. develop fewer cardiovascular problems later in life than those who enter the Land of Nod both before or after this golden hour.

The paper detailing the finding, published in the European Heart Journal this month, is co-authored by David Plans, who is a researcher at Huma, a healthcare technology company, and a fellow at the Alan Turing Institute.

Plans and his team did their analysis using one week’s worth of data on sleep times and six years of subsequent medical histories for more than 88,000 people.

Of the study participants, those who fell asleep between 10 p.m. and 11 p.m. had a lower incidence of heart problems in later life. In contrast, participants who usually dozed off between 11 p.m. and midnight had a 12-percent higher risk of heart problems later in life. The later people stayed up, the higher the chances of cardiovascular issues: People who fell asleep after midnight had a 25-percent higher risk of heart problems, according to the study.

Curiously, going to bed earlier than 10 p.m. was also correlated with an increased risk of cardiovascular illness. Study participants who fell asleep before 10 p.m. had a 24-percent higher risk of a heart problem later than did those who fell asleep during the 10 p.m. to 11 p.m. window.

“[T]he findings of this article do not show causality,” the report notes, but rather they “suggest a relationship between [sleep onset time] and risk of developing [cardiovascular diseases], particularly in women,” who made up 58 percent of the study sample.

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Science in Action — The data in this study comes from the U.K. Biobank, a hulking depository including health and other information on 500,000 Britons to be collected over 30 years.

From 2013 to 2015, more than 100,000 of these participants wore a Fitbit-like activity tracker for seven days, providing researchers with data on both their activity and sleep patterns.

Plans’ team used data from a select population of 88,026 people included in the initial group — some were excluded for incomplete data and others for health issues that might affect sleep. The sample population ranged in age from 43 to 79, with an average age of 61. Fitty-eight percent of the study group were women.

Plans and his team then tracked the participants’ cardiovascular health over the course of six years using health information collected as part of the BioBank. They found that 3.6 percent — or 3,172 participants — reported some kind of cardiovascular disease diagnosis during that time, including strokes and heart attacks.

However, people who fell asleep during 10-to-11-p.m. had the lowest occurrence of heart problems. Importantly, sleep duration, quality, and other measures were controlled for in this study, isolating the time someone went to sleep as the crucial factor.

How this affects longevity — It is hard to overstate the threat of cardiovascular disease in shortening lifespans. Heart problems are the leading cause of death globally, killing about 17.9 million people every year, about a third of them younger than 70.

This study is novel because of its large sample size and for isolating the time at which one goes to sleep as potentially linked to heart health apart from other factors, like the duration and quality of sleep. Importantly, the study does not answer why sleep timing is tied to cardiovascular health outcomes.

“[T]he findings of this article do not show causality,” the report notes, but rather they “suggest a relationship between [sleep onset time] and risk of developing [cardiovascular diseases], particularly in women,” who made up 58 percent of the study sample.

Why it’s a hack — It’s important to note that the study did not try to prove causality. Middle-aged people who get to bed around 10 p.m. might have other daily habits, genetic factors, or other influences that play into their heart health, like lower stress or fewer work hours.

Scientists do think sleep plays a role in heart health, however. During sleep, one’s blood pressure drops and the heart relaxes along with the rest of the body.

“Evidence suggests circadian rhythm disruption could be an understudied risk factor for [cardiovascular diseases],” the study states, “and that prolonged misalignment of circadian rhythms is associated with elevated blood pressure,” among other risk factors for heart disease.

But to fully understand the factors at play “further research in large samples more representative of the global population is required,” the study authors conclude.

HACK SCORE — 🌛🌛🌛🌛🌛🌛 (6/10 sweet dreams)

Abstract:

Aims

Growing evidence suggests that poor sleep health is associated with cardiovascular risk. However, research in this area often relies upon recollection dependent questionnaires or diaries. Accelerometers provide an alternative tool for measuring sleep parameters objectively. This study examines the association between wrist-worn accelerometer-derived sleep onset timing and cardiovascular disease (CVD).

Methods and results

We derived sleep onset and waking up time from accelerometer data collected from 103 712 UK Biobank participants over a period of 7 days. From this, we examined the association between sleep onset timing and CVD incidence using a series of Cox proportional hazards models. A total of 3172 cases of CVD were reported during a mean follow-up period of 5.7 (±0.49) years. An age- and sex-controlled base analysis found that sleep onset time of 10:00 p.m.–10:59 p.m. was associated with the lowest CVD incidence. An additional model, controlling for sleep duration, sleep irregularity, and established CVD risk factors, did not attenuate this association, producing hazard ratios of 1.24 (95% confidence interval, 1.10–1.39; P < 0.005), 1.12 (1.01–1.25; P= 0.04), and 1.25 (1.02–1.52; P= 0.03) for sleep onset <10:00 p.m., 11:00 p.m.–11:59 p.m., and ≥12:00 a.m., respectively, compared to 10:00 p.m.–10:59 p.m. Importantly, sensitivity analyses revealed this association with increased CVD risk was stronger in females, with only sleep onset <10:00 p.m. significant for males.

Conclusions

Our findings suggest the possibility of a relationship between sleep onset timing and risk of developing CVD, particularly for women. We also demonstrate the potential utility of collecting information about sleep parameters via accelerometry-capable wearable devices, which may serve as novel cardiovascular risk indicators.