Sleep is vital for good health but more of it may not always be better for everyone. Research recently published in the journal Neurology has found middle-aged and older people who sleep more than eight hours a day have an increased risk of stroke.
The findings are presented alongside a meta-analysis of 11 other studies from across seven countries involving over half a million people, which also finds longer sleeps can land you in an early grave.
Sleep and stroke
Poor sleep is a significant health concern because it's known to affect emotional and cognitive well-being, quality of life, work-related productivity and safety. But insomnia itself is not associated with higher rates of premature death, according to a US study of more than 1.1 million people aged between 30 and 102 years. Rather, it's sleep that is habitually either too short or too long that may be problematic.
The authors of the Neurology paper asked almost 10,000 people aged between 42 and 81 the average number of hours they slept daily and whether they generally slept well. Participants answered these questions twice in a four-year period and were monitored for nine-and-a-half years to see whether or not they had a stroke.
After adjusting for age and sex, researchers found long sleeps (more than eight hours) were associated with a significant (45 per cent) increase in the risk of stroke. What's more, being a good sleeper for those long hours in bed didn't protect against this increased risk.
Short sleeps of less than six hours a night were associated with a 19% increased risk of stroke. It seems there's a U-shaped relationship between sleep and stroke risk, with higher risk for sleep durations on either side of the six- to eight-hour band.
It's how long you sleep, rather than how well, that's associated with the higher mortality risk and higher risk of stroke. But, as the authors of the Neurology paper point out, unmeasured sleep disorders, such as obstructive sleep apnoea, may be playing a role in their finding, especially among long sleepers.
The golden mean
We know that as many as 72 per cent of surviving stroke patients have sleep apnoea. The condition makes a night's sleep lighter as the sleeper repeatedly moves from deep to light sleep, to help them breath. For those with untreated sleep apnoea this may translate to a longer, lighter night's sleep, rather than a shorter, deeper sleep, which seems ideal.
Of course, an association between two things doesn't necessarily mean one causes the other. Researchers are still debating the question of whether short and long sleep duration are the cause, consequence or early markers of poor health.
Earlier research reports suggest long sleeps may be related to a range of physical factors, such as increased inflammatory biomarkers or certain cardiovascular conditions, but the UK paper provides no support for these suggestions. Its finding of the relationship between sleeping for more than eight hours and stroke risk was robust across healthy people and those with a range of pre-existing illnesses.
The paper's authors say we need to know more before prolonged sleep can be taken to be a useful clinical marker for increased stroke risk, and before we can understand what mechanisms may be operating. At an individual level, it remains an open question as to whether deliberately changing how much you sleep will change your risk of stroke.
Perhaps the saying of "eight hours work, eight hours play and eight hours sleep" per day should be modified to suggest that, for most of us, closer to seven hours sleep each day might be healthiest. After all, we know from population-based studies that include hundreds of thousands of people that more sleep is not always a good thing.
Last month, the US-based National Sleep Foundation published revised guidelines on how much sleep people need based on input from 18 sleep experts and over 300 studies. For those aged between 18 and 65 years, it recommended between seven and nine hours over a 24-hour period.
For those aged over 65, it suggested the narrower band of between seven and eight hours. In the light of the new findings, this narrower band may be the best idea for all adults, not just those aged over 65 years.
Dorothy Bruck is a Professor of Psychology at Victoria University