Too much sleep as harmful as too little, study finds
Sleeping in late isn’t going to make you any sharper during the day.
It might even make you as bad at reasoning as someone who got only four hours of shut-eye.
Researchers at Western University crunched the numbers from more than 10,000 sleep study participants — the largest project of its kind in the world — and found getting too much sleep and sleeping too little equally hamper brain-power.
“We were interested to see, in a large sample of people from around the world, how everyday sleep patterns relate to brain function,” study lead author and neuroscientist Conor Wild said. “There was an overwhelming response when we launched the study.”
The study by Western’s Brain and Mind Institute confirmed a long-held assumption: seven to eight hours of sleep each night is optimum for best brain performance. On brain puzzles and games, people who slept more than that were just as impaired as those who slept less.
More than 10,000 people around the world were included in the study, published in the journal Sleep.
All participants completed a comprehensive online profile, including details not only about their sleep, but also their medications, history of depression or anxiety, age and education.
They were also asked to complete an online cognitive assessment shortly after waking up.
The games and puzzles tested a range of abilities including verbal reasoning, inhibition, short-term memory, spatial working memory and selective attention.
Researchers found the people who slept four hours or less performed cognitive tasks worse then their well-rested counterparts. The same was true for people who over-slept, patterns that held for people of all ages in the study.
Participants’ reasoning and verbal abilities were the two traits most affected by sleep duration. Short-term memory performance was relatively unaffected, the study found.
“It doesn’t seem to affect all brain functions equally. People who didn’t sleep very much actually had no problem remembering things,” Wild said. “It’s people’s ability to solve complex problems and reason through things that seemed to be specifically impaired by too little or too much sleep.”
The study participants were selected from an existing pool of more than 40,000 who signed on to be part of the world’s largest multi-national sleep study. The project was launched in June 2017 by Western researchers.
As for why over-sleeping and under sleeping appear to lead to similar brainpower sluggishness, Wild said it needs to be studied further.
“It’s kind of another thing we want to dig into a little bit more,” he said. “It could be an effect of sleep inertia. If you’ve ever had that feeling of having a really deep, long sleep it might take you awhile to come fully out of that sleep.”
Study authors are planning to look closer at the data collected and use it in future research projects.
“We have a really rich data set here,” Wild said. “There are still some interesting things to be found. We have some more ideas of how to really dig into this data set to test new hypotheses and generate new ideas we can follow up with in the lab.”
Dr. Conor Wild