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We already know sleep is super important, but new research suggests too much of it can, actually, be a bad thing.
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The study found that “long sleepers” were more likely to report symptoms of depression and worse cognitive performance.
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Here’s what you should know about how long you should sleep, with insight from experts.
When you’re struggling to get the recommended seven-plus hours of sleep each night, logging anything more than that sounds like a dream come true. But new research suggests that there is actually a sleep sweet spot you should aim for—and that making sure you don’t sleep *too* much could affect how well your brain works.
The study, which was published in the journal Alzheimer’s & Dementia, specifically discovered that sleeping too much was linked with worse cognitive performance. Here’s why and what the tipping point was, plus how to figure out the best amount of sleep for you.
Meet the experts: Vanessa Young, MS, lead study author and clinical research project manager at the Glenn Biggs Institute for Alzheimer’s and Neurodegenerative Diseases at UT Health San Antonio; W. Christopher Winter, MD, a neurologist and sleep medicine physician with Charlottesville Neurology and Sleep Medicine and host of the Sleep Unplugged podcast
What did the study find?
For the study, researchers analyzed data on cognition and how long people slept in more than 1,800 people without dementia who participated in the Framingham Heart Study, a community-based cohort study of residents in Framingham, Massachusetts. The study specifically focused on people between the ages of 27 and 85.
The researchers found that people who slept for nine hours or more a night had worse cognitive performance. That was especially pronounced in participants with depression, regardless of whether they used antidepressants.
The researchers also discovered that so-called “long sleepers” were more likely to report symptoms of depression and that sleep might be a modifiable risk factor for cognitive decline in people who have depression.
Why is sleeping nine hours or more associated with poorer cognitive performance?
This isn’t the first study to find a link between sleeping for longer periods and lower cognitive performance. “Regularly sleeping more than nine hours a night has been linked to lower cognitive performance in some studies—including ours,” says Vanessa Young, MS, lead study author and clinical research project manager at the Glenn Biggs Institute for Alzheimer’s and Neurodegenerative Diseases at UT Health San Antonio.
There is a “J” curve relationship between sleep and health, points out W. Christopher Winter, MD, a neurologist and sleep medicine physician with Charlottesville Neurology and Sleep Medicine and host of the Sleep Unplugged podcast. What this means is that more sleep isn’t always better. “Generally, the best health outcomes in adults are at seven hours,” he says.
As for why that is, Young says sleeping for longer periods of time is likely “a sign that something else is happening beneath the surface.” That could mean vascular issues, depression, changes in brain health, or something else, she says.
“While we can’t say for certain whether longer sleep leads to worse cognition—or if people with emerging cognitive issues start sleeping more—our findings suggest that unusually long sleep might be worth paying attention to, especially if it’s a change from your normal routine,” Young says.
What is the optimal amount of sleep to get?
First of all, everyone is different and requires different amounts of sleep, but research generally suggests that getting between seven and nine hours of sleep a night is best for cognitive performance.
Still, Dr. Winter stresses that sleep needs are individual and it’s a good idea to pay attention to certain elements of your sleep routine to see what your needs are. He suggests looking at how long it takes for you to conk out at night, along with how you feel during the day.
“If it takes a while to fall asleep, you might be seeking too much time in bed,” Dr. Winter says. “But if you struggle to stay awake during the day or fall asleep rapidly at night, you may not be sleeping enough.”
But Young says you shouldn’t automatically assume that more sleep is better. “Like many things in health, balance is important—and sleep may be just one part of a larger puzzle when it comes to brain health,” she says.
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