Sleep apnea, the breathing disorder that affects millions of Americans with loud snoring and fatigue, also puts them at risk for high blood pressure.
According to a new, national study, people with sleep apnea were more than twice as likely to suffer from hypertension than those who didn't stop breathing. Even at moderate levels of sleep apnea, researchers detected a risk of hypertension. And as the severity of sleep apnea increased, so did the prevalence of high blood pressure.
Scientists have suspected for at least 20 years that sleep apnea was linked with hypertension, and some smaller studies have made indirect connections. But this report, published in today's Journal of the American Medical Association, confirms it.
Though a majority of the roughly 6,100 adults in the study, led by the Johns Hopkins School of Public Health, were overweight, even those of normal weight with sleep apnea had a 1.5 times higher risk of high blood pressure.
"This could have very, very important public health implications," said Dr. James Kiley, director of the division of lung diseases at the National Heart, Lung and Blood Institute. "It could have important implications in terms of how cardiologists approach the treatment and control of hypertension, and how primary care doctors deal with the sleep status of a patient."
High blood pressure and sleep apnea have serious health consequences, and as the number of overweight people in the nation reaches epidemic proportions, these two conditions are becoming increasingly common.
A quarter of American adults have high blood pressure, one of the major risk factors for the country's biggest killer, cardiovascular disease. Roughly 10 percent of women and 25 percent of men have some sort of sleep-disordered breathing, studies show, though like hypertension, many don't have symptoms, and many don't know they have it.
Sleep apnea affects about 12 million Americans. Doctors say it's usually caused by a combination of being overweight and having a narrow airway.
While those affected sleep, the muscles at the base of the throat relax, and can completely collapse, stopping breathing. This wakes them up for a short time, stiffening the throat muscles and restarting breathing.
jv0 An episode like that can happen more than 30 times per hour of sleep, with each pause lasting at least 10 seconds, so people can't fall into a deep sleep.
Over the long term, sleep apnea has been linked to higher rates of heart attack and stroke.
It's unclear yet whether sleep apnea actually causes high blood pressure. Hopkins investigators plan to study that next.
But Dr. Javier Nieto, the study's lead author, said their work may explain why so many overweight people are at increased risk for hypertension: Being overweight predisposes them to sleep apnea, and because of what it does to the body, the apnea may be causing high blood pressure.
"The system which is supposed to be resting during the night is not because of this constant stress to make extra efforts to breathe," explained Nieto, an associate professor of epidemiology at Hopkins.
Experts said people with hypertension who have specific symptoms such as snoring, morning headaches or drowsiness should be tested for sleep problems.
Obesity, high blood pressure and sleep apnea are so intertwined that it's difficult to separate them, experts said, and more studies need to be done.
"This is another sign that sleep apnea is bad for the heart and vasculature, but it does not really explain the large quantity of hypertension out there," said Dr. Thomas E. Hobbins, medical director of the Maryland Sleep Disorders Center, based at Greater Baltimore Medical Center.
"There are many more people with hypertension than have sleep disorders."