We followed them for about 10 years, and what we found was that if they slept less than six or seven hours per night, the incidence of heart attacks went up relatively steeply. People who slept about five hours a night had about a 40 percent higher rate of heart attack than people who slept eight hours a night. Surprisingly, people who slept nine or more hours also had more heart attacks, though there was not as big an effect. Now this doesn't explain why sleeping less or sleeping more caused the problem, but it certainly suggests that there is an important relationship there.
How might sleep deprivation increase risk for heart disease?
I think there are two or three things that may be important. Short-term studies show that with sleep deprivation, the sympathetic 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. And elevated insulin levels and poor blood sugar regulation are major contributors to development of vascular disease, which then can lead to heart disease.
