Harvard Health Letter

By the way, doctor: What is the healthiest amount of sleep?

Q. I heard about a study that found people who sleep six and a half to seven hours a night will live longer than those sleeping eight to nine. What is the right amount of sleep?

A. You're asking an important question, but it's hard to answer, and here's why:

Consider the perfect study to answer the question. First, you would recruit a large number of people — say, about 100,000. Then you'd randomly assign some of them to sleep five hours a night, others six, others eight, and so on. You'd also have to figure out some way to make sure people stick with their assigned sleep amounts. Then you'd carefully monitor the health of the study participants — for decades.

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