'Sleep-disordered breathing after adjustment for age and sex is related to significantly increased odds of suffering a stroke over the next four years.'

Sleep-disordered breathing, or sleep apnea, is one of a group of serious sleep disorders in which a person repeatedly stops breathing long enough to reduce the amount of oxygen in the blood and to increase the amount of carbon dioxide.

Researchers categorize its severity according to the number of times per hour that a person stops breathing for 10 seconds or more. Moderate to severe sleep apnea is defined as 20 or more of these events per hour.

Sleep-Disorder Research Results

T. Douglas Bradley, MD, of the Toronto General Hospital/ University Health Network and colleagues analyzed research results from 1,475 subjects who were tested for sleep-disordered breathing at the University of Wisconsin General Clinical Research Center in Madison. Follow-up visits conducted at four-, eight- and 12-year intervals.

During the study and subsequent visits, researchers gave participants a laboratory sleep test (polysomnography), measured their blood pressure and serum cholesterol levels, and checked other stroke risk factors, including body mass index.

Of the 1,475 participants, 76 percent (1,121) did not have sleep-disordered breathing (less than 5 events per hour), 17 percent (251) had a mild disorder (5 to 19 events) and 7 percent (103) had a moderate to severe problem.

Twenty-one individuals suffered a first-ever stroke at an average age of 53.

Increased Odds of Suffering a Stroke

"Our longitudinal analysis provides the first prospective evidence that sleep-disordered breathing after adjustment for age and sex is related to significantly increased odds of suffering a stroke over the next four years," says Dr. Bradley.

Stroke is an important public health issue, he noted, because it constitutes the commonest cause of long-term disability in the United States, affecting more than 1.1 million persons. Its direct and indirect costs are estimated at $56.8 billion for 2005.

"Although our analysis cannot shed light on the pathway by which sleep-disordered breathing affects stroke risk, these novel findings add justification to considering the problem as a condition that either precedes or may contribute to the development of stroke," Dr. Bradley adds.

In the future, randomized clinical trials will be required to determine whether treatment for sleep-disordered breathing could either prevent stroke or improve its outcome, Dr. Bradley suggests.