We all know we feel better when we’re well-rested, but why do we sleep? And how much is enough?
Meir Kryger is a professor in the Yale School of Medicine. He has treated more than 30,000 patients and wrote the book – or at least edited the most widely used textbook – on sleep medicine. Now, he’s written a book for everyone.
It’s called The Mystery of Sleep.
Here are some highlights of our conversation:
Why do we sleep?
We don't know all the answers, and sleep is not just one state. Most of us will spend about 20 to 25 percent of the night dreaming. The rest of the night, we're in what's called non-REM sleep. During non-REM sleep our body repairs lots of things. It repairs tissues and really keeps us going. For example, growth hormone in humans is secreted primarily during that state.
How much sleep is enough?
The amount of sleep that someone needs is a very personal thing it varies from person to person. The average American only sleeps somewhere around six and a half hours a night, and probably needs somewhere between seven and nine hours a night. So, a very large percentage of the American population – maybe even half of the adult population – is chronically sleep deprived, which is one of the reasons why whenever you go into any office anywhere in the U.S. there's always a coffee machine and people hovering around the coffee machine early in the morning.
How common are sleep disorders?
There are so many sleep disorders out there and so many people are affected that the numbers just keep going up and up. It has been estimated that somewhere around 50 million Americans have sleep disorders. The estimates are not exactly clear but we know that there are some sleep disorders that are very, very common. Insomnia, for example, is found probably in about 10 to 15 percent of the entire adult population.
What are the health effects of sleep deprivation?
One of the big things that we see is not terrific performance at school or at work. Concentration, memory, making decisions all become much more difficult when someone is sleep deprived and then performance degrades. For example, people who are sleep deprived can fall asleep driving. And there have been many instances of people who have fallen asleep driving and either killed themselves or killed other people. So those are the acute effects. The more chronic effects is that we think that people who have chronic insomnia are much more prone to certain medical conditions, including high blood pressure.
Are these kinds of impacts reversible?
We can actually repair a lot of the damage and many people will sleep in, for example, on weekends. But the most important thing that people can do – and it's really very effective – is to make sleep a priority. In other words, there are many people who believe that sleep is a waste of time. They need to make sleep a priority so that, when they wake up in the morning, they feel wide awake and alert and ready to face the day.