Longevity Briefs: Waking Up At The Same Time Each Day May Prevent Heart Problems

Longevity briefs provides a short summary of novel research in biology, medicine, or biotechnology that caught the attention of our researchers in Oxford, due to its potential to improve our health, wellbeing, and longevity.

The problem:

We know that as people age, they spend less time asleep each night. Their sleep quality is also reduced: they wake up more frequently during the night and, when their brain activity is measured, studies show that they spend less time in the deeper restorative phases of sleep. These changes correlate with increased risk of multiple age-related diseases, though it’s not clear to what extent sleep disruption causes disease.

Another factor when it comes to sleep is regularity: waking up and getting to sleep at the same time each day. While we typically think of sleep duration as being the main determinant of healthy sleep, research suggests that irregular sleep patterns may actually be more strongly related to mortality than insufficient sleep. This study set out to investigate this further, using wrist accelerometers to objectively measure sleep patterns.

The discovery:

The study included over 72,000 participants from the UK biobank, a large database gathering anonymised genetic, health and lifestyle information and in which participants are followed up for 30+ years. Participants included in this study were aged 40–79 and had worn wrist accelerometers for 7 days. This allowed researchers to calculate a Sleep Regularity Index (SRI) and classify participants as irregular, moderately irregular or regular sleepers.

The researchers found that those with irregular sleep patterns were 26% more likely to suffer a major adverse cardiac event (such as heart attack or stroke) than people classified as regular sleepers. Those with moderately irregular sleep patterns were 8% more likely to suffer an adverse event. When looking at the Sleep Regularity Index, the association with cardiac risk was close to linear – the worse their SRI score, the more likely participants were to suffer a major cardiac event.

Of course, participants with less regular sleep patterns may also have been sleeping less. When researchers took into account whether or not participants were meeting sleep duration guidelines, they found that moderately irregular sleep no longer had a significant impact, but irregular sleep did. Even in people getting the recommended amount of sleep, irregular sleep was associated with a 19% increased risk of major cardiac events compared to regular sleep.

The implications:

It seems as though regularly getting to sleep and waking up at the same time each day is associated with a significantly reduced risk of cardiovascular problems, regardless of whether or not you are getting enough sleep. Sleep regularity also seems to be a ‘continuum’ – the less regular your sleep, the more at risk you are. However, we have to remember that this study can only prove correlation, so while irregular sleep may have caused subsequent cardiovascular events, it’s also possible that some other, unaccounted for factors are affecting both sleep regularity and cardiovascular risk. It’s also worth noting that this study did not measure napping, so we do not know how this factors in to sleep regularity.

As for how sleep regularity influences cardiovascular health, it’s likely to be due to circadian misalignment – that is, when the body’s internal biological clock is out of synch with the environment. The body uses certain environmental cues such as light, temperature and food timing to ‘set’ its biological clock, which in turn regulates the release of hormones, immune function, metabolism and more. Too much day-to-day variation in these cues could disturb these functions, contributing to cardiac risk factors like elevated stress hormones and blood pressure, inflammation and increased blood sugar.