Although previous studies have suggested links between sleep apnea and stroke, it was never clear whether the increased risk of stroke was related to such other factors as hypertension or diabetes. Now, in a study published in The New England Journal of Medicine in November, a Yale team has found that, regardless of other factors, sleep apnea can put people at risk for stroke—the third leading cause of death in the developed world.

“Our study shows that sleep apnea doubles the risk for development of stroke and death, and severe sleep apnea more than triples the risk,” said H. Klar Yaggi, M.D., assistant professor of medicine and principal investigator of the study. “We know that this risk was independent of other risk factors, including high blood pressure.”

As many as one in five adults in the United States suffer from sleep apnea, which causes them to stop breathing temporarily while they sleep. Their bed partners may notice such symptoms as loud snoring, gasping or pauses in breathing. Men are more at risk for sleep apnea than women; obesity is also a risk factor.

The new study, conducted between January 1997 and December 2003, enrolled 1,022 patients over the age of 50 who had gone to the Yale Center for Sleep Medicine for treatment. About 68 percent, 697 patients, had been diagnosed with obstructive sleep apnea syndrome. Hypertension, diabetes and obesity were more prevalent in this group. The mean apnea-hypopnea index—the number of episodes of breathing cessation per hour—of those with the syndrome was 35. Those in a comparison group who did not have obstructive sleep apnea syndrome had a mean index of 2.

An unadjusted analysis found an association between obstructive sleep apnea syndrome and stroke or death from other causes. Age and diabetes, for example, were significant factors. But even after adjusting for age, sex, race, smoking, alcohol consumption and diabetes or cardiovascular disease, the study still found a significant link between sleep apnea and stroke or death. Only 16 in the comparison group suffered stroke or death, but 72 patients with obstructive sleep apnea syndrome had a stroke or died.

The study was supported by the National Institutes of Health, the Department of Veterans Affairs and the Yale Center for Sleep Medicine.