Of all the reasons to get a good night's sleep, protecting your heart might not be top of mind. But maybe it should be. Sleep duration has decreased 1.5 to 2 hours per night per person in the last 50 years. But several recent studies show links between shortened sleep duration, defined as less than six hours of sleep, and increased risk of heart disease.
A 2011 European Heart Journal review of 15 medical studies involving almost 475,000 people found that short sleepers had a 48% increased risk of developing or dying from coronary heart disease (CHD) in a seven to 25-year follow-up period (depending on the study) and a 15% greater risk of developing or dying from stroke during this same time. Interestingly, long sleepers -- those who averaged nine or more hours a night -- also showed a 38% increased risk of developing or dying from CHD and a 65% increased risk of stroke.
Researchers caution that the mechanisms behind shortened and prolonged sleep and heart disease aren't completely understood. "Lack of sleep doesn't necessarily cause heart disease," says Phyllis Zee, MD, PhD, professor of neurology and director of the Sleep Disorders Program at Northwestern University's Feinberg School of Medicine. "It really increases the risk factors for heart disease."
Sleep Loss and Heart Disease
One 2008 study from the University of Chicago found a link between shortened sleep and increased coronary artery calcification (calcium deposits), "a good predictor of subsequent coronary artery disease," says researcher Diane Lauderdale, PhD, professor of epidemiology at the university's Pritzker School of Medicine.
Lauderdale's study also revealed that shorter sleep predicted worsening hypertension (high blood pressure). "For most people, blood pressure falls at night," she says, "so it could be that with shorter sleep it's just not enough for that dip to take place."
But can you reverse this trend? Researchers aren't sure. Part of the reason is that sleep's effects on the heart are a relatively new area of study. Another is that measuring sleep is complicated. Many sleep studies rely on self-reporting, which may not always be accurate. Having your sleep measured objectively involves wearing an activity monitor, which "very likely changes your usual sleep," Lauderdale says.
Bottom line? "It's pretty safe advice for the majority of people that sleeping less than six hours a night is probably not good," Lauderdale says.
How Sleep Helps the Heart
How can getting enough sleep protect your heart? Sleep expert Phyllis Zee, MD, PhD, explains.
- Good-quality sleep decreases the work of your heart, as blood pressure and heart rate go down at night.
- People who are sleep-deprived show less variability in their heart rate, meaning that instead of fluctuating normally, the heart rate usually stays elevated. "That is not a good sign," Zee says. "That looks like heightened stress."
- Lack of sleep can increase insulin resistance, a risk factor for the development of type 2 diabetes and heart disease.
- Shortened sleep can increase CRP, or C-reactive protein, which is released with stress and inflammation. "If your CRP is high, it's a risk factor for cardiovascular and heart disease," says Zee. Shortened sleep also interferes with appetite regulation. "So you may end up eating more or eating foods that are less healthy for your heart," Zee says.