Daniel Kripke, co-director of research at the Scripps Clinic Sleep Center in La Jolla, Calif., compared death rates among more than 1 million American adults who, as part of a study on cancer prevention, reported their average nightly sleep totals. He recently discussed the results of his findings in an interview with Time magazine.
According to Kripke, "Studies show that people who sleep between 6.5 hr. and 7.5 hours a night, as they report, 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 8 hours. Sleeping 8.5 hours might really be a little worse than sleeping 5 hours."
I've seen this even 20 years ago in my health books so this is not new evidence.
He added that risks for various illnesses, such as depression, obesity, heart disease and diabetes increase both with not enough and too much sleep. 'Morbidity [or sickness] is also ëu-shaped,' in the sense that both very short sleep and very long sleep are associated with many illnesses."
Finally, getting out of bed when you're not sleepy and restricting your time in bed actually helps you to sleep more. Kripke noted this helps people get over their fear of the bed. "Spending less time in bed actually makes you sleep better. It is, in fact, a more powerful and effective long-term treatment for insomnia than sleeping pills."