So many of us seem to not get enough sleep, and then there are those that sleep and sleep. But .. it seems the sweet spot for sleep and our brain health (cognitive performance) is about 7 to 8 hours - at least according to a large study from Canadian researchers at Western University. People reporting typically sleeping 4 hours or less a night had the most impairments in how they performed on a variety of cognitive tests - equivalent to aging 8 years.
Reasoning, verbal skills, and overall cognition were impaired by less than 7 hours or more than 8 hours of sleep. But not short term memory. Actual age of the person made no difference on the results - everyone performed best at 7 to 8 hours of sleep. (Volunteers completed a series of 12 tests online which measured a broad range of cognitive abilities.) By the way, about half of the 10886 persons participating in the study reported typically sleeping 6.3 hours or less a night. Not enough. The good news is that just one night of sleeping a little more than the usual too little had a positive effect on cognitive abilities - thus cognitive improvement. From Science Daily:
Preliminary results from the world's largest sleep study have shown that people who sleep on average between 7 to 8 hours per night performed better cognitively than those who slept less, or more, than this amount.
The world's largest sleep study was launched in June 2017 and within days more than 40,000 people from around the world participated in the online scientific investigation, which includes an in-depth questionnaire and a series of cognitive performance activities.
"We really wanted to capture the sleeping habits of people around the entire globe. Obviously, there have been many smaller sleep studies of people in laboratories but we wanted to find out what sleep is like in the real world," says Adrian Owen, Western's superstar researcher in Cognitive Neuroscience and Imaging. "People who logged in gave us a lot of information about themselves. We had a fairly extensive questionnaire and 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."
Approximately half of all participants reported typically sleeping less than 6.3 hours per night, about an hour less than the study's recommended amount. One startling revelation was that most participants who slept four hours or less performed as if they were almost nine years older.
Another surprising discovery was that sleep affected all adults equally. The amount of sleep associated with highly functional cognitive behaviour was the same for everyone (7 to 8 hours), regardless of age. Also, the impairment associated with too little, or too much, sleep did not depend on the age of the participants.
Participants' reasoning and verbal abilities were two of the actions most strongly affected by sleep while short-term memory performance was relatively unaffected. This is different than findings in most scientific studies of complete sleep deprivation and suggests that not getting enough sleep for an extended period affects your brain differently than staying up all night.
On the positive side, there was some evidence that even a single night's sleep can affect a person's ability to think. Participants who slept more than usual the night before participating in the study performed better than those who slept their usual amount or less.