How many hours of shuteye is best? Here’s what the latest science says about sleep

With the release of two studies attempting to unravel the relationship between sleep and brain health, specialists are offering some reassurance to anyone concerned about optimizing their sleep.

New research published Monday suggests that getting less than the recommended seven or eight hours of sleep a night isn’t as damaging as expected to some people’s brains.

That follows a study published last week that suggests daytime naps may have some positive effects.

But sleep science is still a relatively new field, and much more research needs to be done on how sleep patterns intersect with human health, according to a range of Canadian experts who were not involved in the two new studies.

The evidence so far suggests that sleep needs can be very different for different people, said Dr. Elliott Lee, a sleep specialist at The Royal, Ottawa’s mental health center.

“If you find that your sleep pattern is good for you, then I think that’s OK,” he told CBC News.

That is an opinion shared by Dr. Ram Randhawa, a psychiatrist with the University of British Columbia sleep disorders program.

“My best advice is don’t worry… Get away from all this news, stop being so fixated on sleep performance,” he told CBC News.

“Don’t judge your sleep based on what should be perfect or ideal sleep. Everyone is different.”

“No one-size-fits-all rule” for naps

Chronically poor sleep can have serious consequences for physical and mental health, according to Dr. Michael Mak, a sleep medicine specialist at the Center for Addiction and Mental Health in Toronto. It has been linked to cardiovascular problems, high blood pressure, high cholesterol, obesity, depression and anxiety.

What exactly constitutes good sleep habits is still up for debate. The growing interest in the benefits of a healthy snooze has fueled a thriving industry, offering everything from wearable technology that tracks your hours of sleep or soothes you with gentle vibrations, to weighted blankets and bed cooling systems.

Taking a nap is something that sleep doctors have traditionally advised their patients against, according to the specialists consulted for this story. The thinking was that daytime sleep contributes to patients’ sleep problems at night.

But, Mak said, “there’s no one-size-fits-all rule when it comes to naps.”

a June 19 paper in the journal Sleep Health suggests a modest association between increased brain volume and people who reported napping regularly. The volume of a person’s brain tends to decrease with age, and shrinking faster is associated with memory problems and dementia.

The international team behind the study used information from the UK Biobank, a database containing a wide range of biomedical information from 500,000 volunteers.

Interestingly, the scientists found no link between habitual napping and reaction time, visual memory, or the volume of the hippocampus — a part of the brain essential for memory.

But the greater total brain volume in habitual naps “might suggest that regular naps provide some protection against neurodegeneration by compensating for poor sleep,” the researchers wrote.

Dr. Brian Murray, chief of neurology at Sunnybrook Health Sciences in Toronto, pointed out that previous studies have also shown that naps can help with the cognition of people learning new things.

“People can practice learning a new skill all day, and then they take a nap and get much better. So there’s something about sleep that helps consolidate and organize the brain,” he said.

However, the new research raises some important questions. It didn’t look at how long habitual nappies sleep or what time of day they do it — both factors doctors say could affect results.

Mak described the results as interesting and worthy of further investigation, but he cautions against taking naps for more than 20 minutes at a time. Any longer can lead to a state of disorientation and mental slowness that scientists call sleep inertia.

“If you feel dizzy and sleepy during the day, you might choose to take a short nap and if you respond well to that, that might be something you do occasionally,” Mak said.

Randhawa noted that naps are common in many cultures around the world, but anyone who dislikes an afternoon nap shouldn’t feel compelled to change their routines.

“The people who nap, nap…not just because they want to, because it’s a preference or a choice, but also because they find it relaxing, they like it, they find it restorative,” he said. Randhawa.

“Trying to force yourself to take a nap will only result in you lying in bed frustrated.”

He also cautions against reading too much into studies like this one, saying the reasons for a correlation between naps and brain health are far from clear.

Study raises questions about length of nighttime sleep

The second study, published Monday in the Journal of Neuroscience by a team of European researchers, looked at how brain function is affected by shorter sleep at night.

It is based on data from a number of biomedical databases, including the UK Biobank, which compares self-reported sleep with brain MRIs and cognitive tests.

The researchers found that people who slept less than six hours per night and reported no daytime sleepiness or sleep disturbances had larger regional brain volumes compared to people who slept seven to eight hours, or those who slept less but also had trouble sleeping.

At the same time, however, tests showed slightly lower cognitive function across the board for people who sleep less than six hours a night.

“This indicates that sleep needs are individual and sleep duration per se is very weak or at all related [to] brain health, while daytime sleepiness and sleep problems may show slightly stronger associations,” the authors wrote.

Lee said these results shouldn’t be applied too broadly, noting that the more encouraging findings for short sleepers involved only a small fraction of the samples in the study — 740 of the more than 47,000 people.

For the vast majority of people, seven to nine hours of sleep per night is still ideal, he said.

“Anything under six hours… fairly consistent, except for a small minority of people, can indicate problems in cognitive function [and] reaction time, compared to their baseline,” Lee said.

Murray said the amount of sleep a person needs to function properly can vary greatly from person to person. In some cases, genes play a major role.

“For example, there are mutations that lead to very short sleep, so people can get by with quite a few hours less — maybe four hours,” he said.

“Others are late sleepers, so there are extreme variations.”

Ultimately, though, Murray said research like this exposes some challenges in studying sleep. Both of these recent studies were based on self-reported sleep habits data rather than objective measures.

“It’s actually impossible for people to look inside, to think about what their sleep is like, because they’re not aware of that state,” he said.

“Sometimes people’s perceptions of what happened are very different.”