A neuroscientist explains the power of sleep

Neuroscientist Matthew Walker believes that lack of sleep is the greatest public health challenge we face in the 21st century. He says the lack of sleep is making us sick, making us fat and making us dumb.

In 1942, the average American adult was sleeping 7.9 hours. A recent survey shows that they are are now sleeping about six hours and 31 minutes.

"It took mother nature 3.6 million years to put this thing called eight hours of sleep for human beings in place," Walker said. "And then we come along and lop off maybe 25 percent of that within the space of just 75 or 80 years."

And that trend has had a serious effect on our health. Deadly diseases, obesity and suicide rates all have a connection to how much sleep we are getting, Walker said. In the case of obesity, lack of sleep leads to over-eating because the hormone that usually tells your body when you are full and signals to stop eating is blunted by lack of sleep, he said.

If that wasn't bad enough, the hormone that tells us when we're hungry is amplified by lack of sleep.

"You could say, 'Well if I'm not sleeping as much it must mean I'm awake longer, so maybe I'm just topping off the extra energy that I'm burning,'" Walker said. "Not true." You only burn about an extra 140 calories laying on a couch staying awake for 8 hours than you would losing consciousness there.

You're also more likely to go for junk-food when you're sleep deprived. Reward centers in the brain light up when you're tired, while the rational control regions of the brain shut down.

Obesity is dependent on a lot of other factors, but sleep does have a notable impact. "If you fight against biology, usually you lose," Walker said.

Walker is the author of "Why We Sleep: Unlocking the Power of Sleep and Dreams." He's a professor of neuroscience and psychology at the University of California, Berkeley and the director of the Sleep and Neuroimaging Laboratory. Previously he was a sleep researcher and professor at Harvard University and the founder of the Center for Human Sleep Science.

He spoke Oct. 26, 2017 at the Commonwealth Club of California. The moderator is Alison van Diggelen of the BBC.