How much to sleep
Seven hours; no more, no less. Also, 7 other things worth knowing today.
We've heard it all before, probably since childhood: The adult human brain needs eight or nine hours of sleep per day to perform effectively.
But, a massive study of more than 500,000 people suggests that if you're between 38 and 72 years old, and you're interested in things like improved memory, greater focus, and better problem-solving and decision-making abilities, then eight to nine hours of sleep might actually be a little bit too much.
Writing last May in the journal, Nature Aging, scientists said they examined data from the UK Biobank, which is a government health study involving British volunteers with data going back to 2006, and found that the sweet spot for sleep might be seven hours.
The authors were associated with the Institute of Science and Technology for Brain-Inspired Intelligence at Fudan University in Shanghai and the Behavioural and Clinical Neuroscience Institute at the University of Cambridge.
What I find especially compelling about this study is that it focused squarely on the participants' brains, as opposed to focusing on other sleep health issues. Participants were asked about their sleep habits along with questions about their mental health and well-being, and they also took part in a series of cognitive tests.
Additionally, for about 40,000 of the 500,000 participants, brain imaging and genetic data were also available.
Those who got either too much or too little sleep tended to do worse on tests measuring mental processing speed and visual attention, to demonstrate worse memory and problem-solving skills, and to have more symptoms of anxiety and depression.
As the researchers put it in a statement accompanying their research:
Seven hours of sleep per night was the optimal amount of sleep for cognitive performance, but also for good mental health, with people experiencing more symptoms of anxiety and depression and worse overall well-being if they reported sleeping for longer or shorter durations.
Consistency was important, too; it wasn't a matter of averaging seven hours (with 10 hours one night and four the next), but instead actually hitting the magic number of seven hours habitually. And the magic number of "seven hours" kept coming up:
"For every hour that you moved away from seven hours you got worse," said co-author Barbara Sahakian of Cambridge University's department of psychiatry, although she added that the question why of too much sleep had negative effects is a bit of a mystery. "We don't really understand why sleeping longer would be a problem."
"While we can't say conclusively that too little or too much sleep causes cognitive problems, our analysis looking at individuals over a longer period of time appears to support this idea," another study co-author, Jianfeng Feng of Fudan University in China, said.
We should also be careful about questions of causation versus correlation here. For example, in terms of the seven-hour sleep target, it might be that people who sleep less are more likely to report mental health and well-being difficulties.
Or, it also might be that people who have mental health challenges might sleep more or less or more as a result of those challenges.
Worth noting: It's not far off from a Canadian study from a few years ago that suggested that "the optimum amount of sleep to keep your brain performing at its best was between seven to eight hours every single night."
Also, remember, we're talking about adults here; for kids, the sleep sweet spot is still closer to 9 hours.
One striking thing that people have noticed recently is the degree to which sleep results in practical, physical processes, explaining, for example, things like:
why it's not only physically difficult to "make up" a sleep debt, but that one side-effect of lack of sleep is in fact a loss of the subjective ability to recognize just how tired you actually are, and
the physical changes people can make to train themselves to become "morning people," and why they should consider doing it.
There's nothing more fascinating than the human brain, and the unexpected ways in which it works, and the topic of sleep health, memory, and brainpower are always at the top of the list.
And, if aiming for a consistent seven hours might be associated with better memory, cognition, problem-solving, and mood, it might just be worth the effort.
7 other things worth knowing today
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