The peer-reviewed study published Wednesday in Neurology, the medical journal of the American Academy of Neurology, involved close to 4,500 participants globally, and examined the link between poor sleep and stroke.
People who consistently got less than five hours of sleep were three times more likely to have a stroke than those who get seven hours of sleep on average, the study found. And those who get more than nine hours of sleep were twice as likely to have a stroke than those who got seven hours of shut-eye.
The researchers defined sleep problems as getting too much (more than nine hours) or too little sleep (less than five hours), taking long naps, having poor quality sleep, snoring, snorting and sleep apnea.
“Not only do our results suggest that individual sleep problems may increase a person’s risk of stroke but having more than five of these symptoms may lead to five times the risk of stroke compared to those who do not have any sleep problems,” lead author Christine McCarthy, department of medicine at the University of Galway, said in a media release.
“Our results suggest that sleep problems should be an area of focus for stroke prevention.”
Napping can affect stroke risk too, study found
Participants of the study were asked about their sleep behaviours including how many hours of sleep they got, sleep quality, napping, snoring, snorting and breathing problems.
The authors noted that the limitation of the study was that people reported their own symptoms of sleep problems, “so the information may not have been accurate.”
Napping for more than one hour or having an “unplanned nap” was also linked with increased ties to a stroke, the study said. It found that participants who took naps longer than one hour were 88 per cent more likely to have a stroke than those who did not.
Meanwhile, the study said naps under one hour or “planned” naps were not associated with increased odds of having a stroke.
Dr. Mark Boulos, a spokesperson for the Heart and Stroke Foundation of Canada, and a sleep neurologist with Sunnybrook Hospital in Ontario, said the study out of Neurology is in line with current literature.
“It’s well recognized that sleep disturbance has always been a risk factor (for strokes), but especially sleep apnea,” he said, noting that sleep apnea is when you repetitively stop breathing overnight.
However, what is weaker, is the association of other sleep disorders with stroke, he added.
“But there is still some evidence that links long and short sleep duration with an increased risk of stroke,” Boulos said.
For example, a 2019 study published in Neurology that analyzed sleep patterns of people in China over six years found that regularly sleeping for more than nine hours at a time and taking long midday naps can increase a person’s risk of stroke.
Boulos called Wednesday’s study “unique,” as previous studies have strongly linked stroke with sleep apnea, and not with other sleep disturbances. However, he noted that because the study is observational, future work needs to be done on the subject.
The researchers also noted there is convincing evidence of an association between obstructive sleep apnea and stroke, and the tie to other disorders or impairments in sleep, “are less certain.”
In the press release, McCarthy said the study results show that doctors “could have earlier conversations with people who are having sleep problems. Interventions to improve sleep may also reduce the risk of stroke and should be the subject of future research.”
Why sleeps impacts health
A 2017 Statistics Canada Health Report recommends seven to nine hours of sleep every night for adults aged 18 to 64 and seven to eight hours for seniors 65 years old and up.
The report also said around one-third of Canadians are not getting enough sleep (less than seven hours every night).
Boulos stressed poor sleep quality isn’t just linked to stroke, but also tied to high blood pressure, diabetes, heart attacks and depression.
“You’re supposed to spend about a third of your life sleeping,” he explained. “So if your sleep quality isn’t good, you’re affecting your vasculature for about a third of your life.”
When people sleep, their blood pressure also decreases relative to when they’re awake, Boulos notes. Sleep disturbances, like insomnia or sleep apnea can interrupt this rhythm, which can strain blood vessels and spike blood pressure.
“And fluctuations in blood levels are harmful to the brain,” Boulos said.
There is another “hypothesis” in regard to sleeping, which is that a good night’s sleep may literally clear the brain.
Boulos was part of a previous 2015 study that demonstrated for the first time in humans that poor sleep quality is linked with enlarged spaces in the brain thought to be tasked with toxin removal.
“It’s almost like a toilet effect, when you sleep it flushes harmful toxins down the toilet. And if the toilet is blocked then you cannot clear those toxins out,” he said.
His study found that people who have poor-quality sleep have a backup of these harmful toxins seen in brain imaging.
For those who are poor sleepers, Boulos recommends getting seven or eight hours of sleep a night (with the exception of being sick, when you should get as much sleep as possible) and practicing good sleep hygiene, such as going to bed and waking up around the same time every day, limiting screen time and not eating or drinking before you go to bed.
“If you’re having sleep problems and you can’t solve them just through changes in habits, you should seek medical attention,” he stressed.
— with files from Meghan Collie and Leslie Young