Very bad, according to the authors of a new book. If you think you're getting by on six hours or less, think again.

By Amanda MacMillan
Updated October 13, 2017
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Sleep expert Matthew Walker has a very serious message for Americans. If you’re regularly sleeping less than seven hours a night, says the professor of neuroscience and psychology at the University of California Berkeley, you’re asking for trouble—trouble being everything from Alzheimer’s disease to diabetes to depression. Walker says that sleep loss is the greatest public health epidemic currently faced by developed nations, and he’s determined to spread the word about its dangers.

In his new book, Why We Sleep: Unlocking the Power of Sleep and Dreams, Walker doesn’t mince words. “The shorter you sleep, the shorter your lifespan,” he writes. He was equally unapologetic in an interview with, saying that anyone who gets less than seven hours a night is committing a “slow form of euthanasia.”

But if skimping on sleep is really so dangerous, why do so many of us do it? And even more importantly, how can we stop? Here’s what Walker wants everyone to know about how sleep affects health, and what you can do to optimize both.

Sleep deprived people don’t realize they’re sleep deprived

People often tell Walker they feel just fine on less than seven hours of sleep a night. “But your subjective sense of how you’re doing when you’re sleep deprived is a miserable predictor of how you’re doing objectively,” he says. “An analogy would be a drunk driver at a bar telling you they’re just fine to drive.”

Then there’s the fact that sleep deprivation, unlike inebriation, usually comes on gradually over many years of staying up later and later or waking up earlier and earlier.

“There was probably a time when you were getting a solid seven or eight hours of sleep, and then modern life and family and work and entertainment started to grip your sleep and squeeze it at both ends,” he says. “People start to reset their baseline, and they think that how they feel normally is as good as it’s going to get.”

The health risks are real

Walker devotes three entire chapters in his book to the “why” we should sleep, detailing the brain and body benefits of a good night’s rest and the risks that go along with cutting that short.

It’s probably not surprising that people who don’t sleep for an entire night perform poorly on reaction and concentration tests the next day. But here’s the most concerning part, he writes: Research shows that it only takes 10 days of sleeping six hours a night (a number that might sound totally acceptable to many of us) to become as impaired as someone who’s gone without sleep for 24 hours straight.

Skimping on sleep can affect other organs in the body, as well. One 14-year study found that men who averaged six hours or less a night were four to five times more likely to suffer one or more cardiac arrests than those who got more. Insufficient sleep has also been linked to diabetes, weight gain, fertility problems, decreased immunity, Alzheimer’s disease, and more.

How to tell if you’re getting enough

“One way to determine if you’re getting enough sleep is to ask yourself: If I didn’t set my alarm, would I sleep past it? If the answer is yes, that suggests that your body’s not done with sleep and it needs more,” says Walker.

You can also gauge how tired you are just a few hours after waking up, and whether you can get by without a cup of coffee. “I looked around on an airplane the other day at 10 or 11 in the morning, and half the people on the plane were fast asleep,” he says. “That should not be physiologically possible if people are getting enough sleep at night.”

He recommends setting aside one week and making time to get at least seven hours every single night, and comparing how you feel at the end of that week with how you feel normally. “One patient described it to me as wiping the fog from a frosted window,” he says. “His mental function was so much clearer when he finally made that change.”

Rules for healthy sleep

As much as Walker thinks that alarm clocks can disrupt much needed sleep, he doesn’t advocate ditching them. One, because most people still need it to wake up and get to work on time. But two, because they’re an important part of Walker’s golden rule for sleep: Wake up at the same time every day.

You should go to bed at the same time every day too, he says, but he realizes that life can get in the way and that doesn’t always happen. “Even if you go to bed late or you have a crummy night of sleep for some reason, don’t sleep in,” he says. “Get out of bed. You may have a bit of a grim day, but it will help you fall asleep better that night and will help you maintain a better pattern in the long run.”

Walker has a few other rules for good sleep, too. The optimal room temperature for sleep is between 65 and 68 degrees, he says—“cooler than most people realize”—because the body’s core temperature needs to drop two to three degrees in order to initiate sleep. Keep the room cool and dark, he recommends, and don’t stay in bed for more than 20 minutes if you can’t fall asleep.

Finally, he recommends no caffeine after 2 p.m., and no alcohol before bed. “Alcohol is a powerful blocker of REM sleep, which is essential to your mental health and also to a variety of your body’s functions,” he says. “I’m not saying you can never have a drink at night, but you should know that it will affect your sleep, and make an informed decision from there.”