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Brief periods of interrupted breathing during sleep affect an estimated 10 to 25 percent of people in the U.S. A smattering of studies have linked the condition, known as obstructive sleep apnea, to a host of serious health risks, such as cardiovascular disease, obesity and even accidents—but long-term, population-based data on mortality overall have been lacking.
A new, 15-year-long study, published online yesterday in PLoS Medicine, followed 6,441 men and women—both with and without the condition—in the National Heart, Lung and Blood Institute's large Sleep Heart Health Study to see if there was any correlation between apnea and a higher risk of death.
During the course of the study, which followed up with subjects after an average of about eight years, 1,047 of the subjects died. After adjusting for age, race, body mass index (BMI) and smoking, the authors found that men ages 40 to 70 with severe apnea (defined as more than 30 incidents of disrupted breathing 10 seconds or longer per hour—8.2 percent of the cohort's men) had about one and a half times higher risk of dying from any cause than those who did not.
The other age, gender and apnea severity groups did not show a statistically significant increased risk, but that doesn't mean they will not be watched carefully. "Our study does not prove that women are not at risk," says Naresh Punjabi, lead study author and an associate professor of medicine at The Johns Hopkins Hospital in Baltimore. Not enough of them died or were ill enough to make a statistically sound connection, but researchers will continue to follow this cohort as long as funding allows, Punjabi notes.
The findings do not come as a surprise to the sleep research community. "It's long been believed that sleep apnea increases the rate of death," says David Schulman, an assistant professor of medicine at Emory University in Atlanta who wasn't involved in the study, noting that those with apnea are more likely to have high blood pressure and elevated cholesterol. But, he cautions, "it's hard to know for sure that apnea causes these diseases." Many of those with sleep apnea, he notes, tend to be male, older and overweight—increasing mortality rates overall—which makes it hard, he says, to conclude, "Was it the apnea, or was it that the guys were overweight and older?"
But the new research does fill an important hole in the data. Crucially, Punjabi notes: "The cohort is not patients. They actually represent individuals, people like you and me…. This is not a clinical study, but more of a community-based study." The authors even excluded those who, during the study, sought treatment for sleep apnea. Perhaps most important, it was a substantial group. "This is really the grandfather of all sleep–heart studies," Schulman says.
Punjabi and others look forward to formal clinical trials, in which researchers can start testing methods of intervention and treatment to see if they can bring the risk of mortality in check. "We do know for sure that treating apnea does make blood pressure better, but not vastly better," Schulman says. "In terms of things that kill people, heart disease is number one in this country," he notes, which makes any link with apnea a crucial line of research. "We'd love to know mechanistically why this happens."
Those with sleep apnea often suffer from increased sleepiness during waking hours, which can be dangerous when driving—or flying. Last year, two crew members overshot their Hawaiian destination on an inter-island flight after falling asleep when the plane was in cruise mode. No one was hurt, but the National Transportation Safety Board (NTSB) ruled that the pilot's undiagnosed sleep apnea was likely one of the causes. The NTSB has since recommended that the Federal Aviation Administration screen pilots for signs or previous diagnoses of the disease.
Another recent study, published last week in the Journal of Clinical Sleep Medicine, found that as many as 94 percent of adults with Down's syndrome had some sort of obstructive sleep apnea—and in 69 percent of those patients it was severe.