How Much Sleep Do You Really Need?

How much sleep do you really need? Sleep is one of the best topics in science today because of its debate on how much we really need it. There’s also debate on how it affects everything from our athletic performance to our income.

Daniel Kripke, co-director of research at the Scripps Clinic Sleep Center in La Jolla, Calif., has looked at the most important question of all. In 2002, he compared death rates among more than 1 million American adults who, as part of a study on cancer prevention, reported their average nightly amount of sleep. To many, his results were surprising, but they’ve since been corroborated by similar studies in Europe and East Asia.

Most studies show that people who sleep between 6.5 hours and 7.5 hours each night live the longest. And people who sleep 8 hours or more, or less than 6.5 hours, don’t live quite as long. There is just as much risk associated with sleeping too long as with sleeping too short.

The big surprise is that long sleep seems to start at the 8th hour. Sleeping 8.5 hours might really be a little worse than sleeping 5 hours. Very short sleep and very long sleep are associated with many illnesses — with depression, with obesity — and therefore with heart disease — and so forth. But the ideal amount of sleep for different health measures isn’t all in the same place.

Most of the low points are at 7 or 8 hours, but there are some at 6 hours and even at 9 hours. People with diabetes are 7-hourr sleepers. But these measures aren’t as clear as the mortality data.

“I think we can speculate [about why people who sleep from 6.5 to 7.5 hr. live longer], but we have to admit that we don’t really understand the reasons. We don’t really know yet what is cause and what is effect. So we don’t know if a short sleeper can live longer by extending their sleep, and we don’t know if a long sleeper can live longer by setting the alarm clock a bit earlier,” Kripke said in a statement.

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