About one-third of Americans sleep 6.5 hours or less a night, according to the National Sleep Foundation. While these Americans may be putting their health at risk, people shouldn’t spend all of their time sleeping, either; research shows that sleeping more than nine hours may also have deleterious effects, although the reasons for this are less clear.
I think there are two or three things that may be important. Short-term studies show that with sleep deprivation, the sympathatic nervous system becomes activated. As a result, your blood vessels constrict and your blood pressure tends to go up. And we think that may play a role in heart disease. Sleep deprivation probably also affects the regulation of blood sugar. If you’re sleep deprived, it requires more insulin to keep your blood sugar where it should be than it does if you’re not sleep deprived.
There have been at least three major studies of huge groups of people to look at the relationship between sleep duration and some of these outcomes, and they’ve all shown that if you sleep too long, you tend to get adverse outcomes. In some cases, the outcome was heart disease.