There are few things better than sleeping in on a weekend morning, but when it comes to snoozing, you really can have too much of a good thing, new research suggests.
The Centers for Disease Control and Prevention (CDC) recommend that adults get seven or more hours of sleep a night.
Health officials say that we are in the midst of a sleeplessness epidemic, and all those short nights raise our risks for all manner of diseases and even of an earlier death.
Plus, getting enough sleep keeps our minds sharper.
Early results from the largest sleep study in the world, conducted by the University of Western Ontario confirmed that getting too little sleep is bad for the brain – but so is getting too much.
People who got more than eight hours of sleep the night before did just as badly on cognition tests as those who got less than seven hours of rest, a new study reveals
More than a third of Americans get less than seven hours of sleep a night, leaving more than 100 million adults groggy, moody and unfocused.
Over time, being chronically underslept also raises the risks of some of the leading causes of illness and death in the US, such as heart disease, high blood pressure, obesity and diabetes.
There is still a great deal we don’t know about sleep and why it is so crucial to survival, but research suggests that one of its functions is as a cleaning period for the brain.
Neuroscientists at the Brain and Mind Institute aim to solve more of the remaining mysteries of our nightly snooze through the largest sleep study ever undertaken.
The first stage of their research has been to survey 40,000 people about their sleep habits, and send them cognition quizzes.
Cognition tests measure things like verbal skills, reasoning and short-term memory.
While memory was relatively stable regardless of sleep times, the researchers found that language skills and reasoning were deeply affected by the amount of sleep their participants got.
As soon as their nightly sleep hours dipped below seven hours, cognition started to decline.
And that was the experience of about half of the participants, who slept less than 6.3 hours a night.
For those who slept four hours or less, the brain effects were even more dramatic.
‘Cognition declines as we get older, and, for those people sleeping four hours or less, it was as if we had aged them almost ten years,’ lead study author Dr Conor Wild, a neuroscientist at University of Western Ontario, told Daily Mail Online.
‘And it goes equally for those who sleep too much,’ he added, noting that this group however, was much smaller.
During sleep, the brain gets a bath in cerebrospinal fluid and (by less clear mechanisms only recently discovered) ‘junk’ proteins associated with Alzheimer’s get taken out.
But with too much sleep, you can experience what scientists call ‘sleep inertia.’
When we wake up as we are supposed, during non-REM sleep, our heart rates are slower, our brain is less active and our blood pressure is lower.
This helps waking up be less of shock to the system.
On the other hand, when you wake up in the middle of REM sleep, there’s a lot of activity that gets interrupted, resulting in sleep inertia and that groggy feeling.
‘When you sleep too much on reg basis have harder time coming out of the fog and cognition is slightly impaired as a result,’ Dr Wild said.
For those who didn’t get enough sleep, even one night of getting the right amount of sleep can restore cognitive function – though it’s unclear how long over-sleepers need to reset.
But for people of all ages, between seven and eight hours of sleep was the ‘sweet spot’ for cognitive performance, said Dr Wild.
As soon as they slept more or less, their scores started to decline.
‘Doctors say that amount of sleep is good for physical health, and now we know that it is going to help cognitive health, too,’ Dr Wild said.