Getting too much sleep can be just as bad for you as getting too little, according to a new study from Western University.
Researchers from the university's Brain and Mind Institute launched what they say is the world's largest sleep study in June of last year. Within days, more than 40,000 people from around the globe signed up to take part.
“We found that the optimum amount of sleep to keep your brain performing its best is seven to eight hours every night and that corresponds to what the doctors will tell you need to keep your body in tip-top shape, as well," said Conor Wild, the study’s lead author. "We also found that people that slept more than that amount were equally impaired as those who slept too little,"
Study participants were asked to fill out an in-depth online questionnaire before completing 12 cognitive performance activities.
"They told us things like which medications they were on, how old they were, where they were in the world, and what kind of education they’d received because these are all factors that might have contributed to some of the results,” said Adrian Owen, a Western researcher in cognitive neuroscience and imaging.
The performance activities participants were subjected to included games and puzzles that test short-term memory, visuospatial working memory, deductive and verbal reasoning, and feature-based attention and concentration.
About half of the participants reported sleeping less than 6.3 hours a night, about an hour less than the study’s recommended amount, and had detectable impairments in overall cognition. For those who slept four hours or less per night, the impairment was the equivalent to adding almost eight years to their age, researchers found.
Participants’ reasoning and verbal abilities were two of the actions most affected by the amount of time spent sleeping. Short-term memory performance was relatively unaffected.
Researchers also found even a single night's sleep can affect a person’s ability to think. People who slept more than usual the night before participating in the study performed better than those who slept their usual amount or less.
"I think we are all keenly aware when we don't get enough sleep you can feel it in your body and you might feel that your brain is slightly foggy, but what we might not realize is that some of our brain functions are more impaired than others," said Wild.
The multi-national sleep study was published in the Oxford Academic journal Sleep.