A team of Western University researchers recently released the results of the world’s largest sleep study, revealing that too much sleep impairs daily cognitive functions just as much as too little sleep.
The study showed the optimum amount of sleep is seven to eight hours per night, based on feedback from around 40,000 people from 173 different countries. Regardless of age, people who sleep less or more than this amount experience selective cognitive impairment to problem-solving and verbal abilities. Other cognitive functions, such as memory, were not significantly impaired.
“We needed lots of people to participate, people from all over the world … so that we could really get a good picture of how different kinds of people sleep and whether or not that had any effect on their day-to-day brain functioning,” said Conor Wild, Western research associate and lead author of the study.
Most significantly, the results showed roughly half the sample, around 20,000 people, were not getting the right amount of sleep, with an average of 6.3 hours per night.
“Those people who don't get enough sleep on a regular basis could be operating day-to-day with impaired problem-solving, reasoning and communication abilities,” explained Wild. “That's a problem for people who have positions of high responsibility or [who are] in charge of making life-saving decisions.”
Further, Wild explained the results contradicted the common perception that people need less sleep as they get older. People of all ages in the study who did not get seven to eight hours of sleep experienced similar cognitive impairment.
He added that a single night of the right amount of sleep was successful in improving cognitive ability, suggesting a fast bounce-back effect.
Wild clarified these findings do not necessarily apply to every single person.
“One caveat to this kind of study is that we're painting in broad strokes, and it's describing trends in the population,” said Wild. “There's lots of other scientific evidence that suggests that different people can be very resilient, or not, to the effects of too much or too little sleep, so that's not to say if you don't get your seven to eight hours every single night you're going to have an impairment.”
Launched in June of 2017, the online study included a questionnaire and 12 cognitive tests. Wild explained the tests were adapted from classic neuro-psychological tests into games that people can play on their phones, tablets or other personal devices.
Wild explained this digital design facilitated large-scale recruitment as in-lab sleep studies can usually recruit 20 to 100 participants, a number that is too small to detect subtle findings.
Wild and colleagues will use the data set from this study in follow-up research, including factors that explain why certain people are particularly vulnerable or resilient to too much or too little sleep.
The study was published on Sept. 13 in the high-impact journal SLEEP.