Getting a good night's sleep does far more than improve your mood and level of alertness the next day. New research shows that sleep may be good for your heart health as well. That means that, along with maintaining a healthy diet and exercising, adequate sleep should be considered a crucial part of a healthy lifestyle.
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. Below, sleep researcher David White, MD, an associate professor of medicine at Harvard Medical School, discusses the complex relationship between sleep and heart disease.
Does sleep affect risk for heart disease?
There is some early evolving evidence that how much you sleep may contribute to heart attacks. We looked a group of 70,000 nurses that had been followed for a long period of time, and we compared how many hours they reported sleeping at night with the number of heart attacks that occurred after they had reported to us how long they slept.
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.
What other sleep problems may be a factor?
Sleep apnea is a condition that is characterized by a collapse of the airway that occurs during sleep. When the airway collapses, eventually the person wakes up to resume breathing, and goes back to sleep and does it again. Obviously, if you have to wake up to breathe, you don't sleep very well.
There's substantial literature suggesting that the falls in oxygen and the elevations in carbon dioxide contribute to the development of heart disease. Sleep apnea clearly contributes to the development of high blood pressure, and it leads to the development of heart attacks, strokes and congestive heart failure as well.
How might sleeping too long be a factor in heart disease?
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. In other cases, it was death. None of the studies have come up with a very good explanation, even in a speculative way.
The one explanation they commonly give is maybe these people have a sleep disorder such as sleep apnea, which causes them to spend more time in bed, and therefore they end up with a medical problem.
I don't personally find that very convincing because I follow lots of patients with sleep apnea and most of them just don't spend nine and 10 hours a day in bed trying to sleep. So it may turn out to be something to do with the effect of inflammatory systems on sleep.
How might inflammation play a role in sleep and heart disease?
There's a little bit of data that sleep deprivation can lead to increases in cytokines that may ultimately turn out to be important in cardiovascular disease. Cytokines are basically chemical mediators to help cells talk to cells. Normally cytokines attract other cells to the area to try to fight the inflammation, but when they start to attack normal tissues, they can have a damaging effect. There's some evolving evidence that inflammation may be important in the development of heart disease. If that's true, that may turn out to be very important.
How important is good sleep for heart health?
There's evolving evidence that getting a reasonable quantity of good quality sleep is important in maintaining health and particularly heart health. That's not to say that if you sleep fewer than six hours or you sleep more nine or more hours, it's going to be the overwhelming variable in the development of heart disease, but it will probably be a contributor along with a variety of other factors.
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