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Moderate and Severe Sleep Apnea Linked to Increased Risk of Stroke

By Linda Little

SAN DIEGO, CA -- May 30, 2005 -- Obstructive sleep apnea significantly increases the risk of having a stroke, researchers reported at the American Thoracic Society (ATS) Annual Meeting.

In a study of 1475 people, subjects with moderate to severe sleep apnea had 3 to 4 times the risk of stroke compared to subjects who did not have sleep apnea, adjusting for age, sex, body-mass index, smoking and alcohol intake.

"The stroke risk that we found for people with moderate to several sleep apnea is quite significant," said Douglas Bradley, MD, Professor of Medicine and Director, Center for Sleep Medicine and Circadian Biology, University of Toronto, Toronto, Canada.

Dr. Bradley and colleagues conducted a prospective analysis of data from the Wisconsin Sleep Cohort Study to determine the relationship between obstructive sleep apnea and stroke risk.

They conducted polysomnographic tests and gathered data on patients' history of stroke and known confounding factors among 1038 subjects in the Wisconsin Sleep Cohort Study. Patients were evaluated at 4 years and 8 years and provided data; 1038 subjects provided 2056 data points at 4 years and 709 subjects provided 1028 data points at 8 years.

The patients were defined as having moderate to severe obstructive sleep apnea if their breathing stopped at least 20 times per hour of sleep. People whose breathing stopped or slowed between 5 and 20 times per hour of sleep were considered to have mild sleep apnea. Patients' age range was 30 to 60 years.

Results show that 22 study participants had a stroke during the first 4-year follow-up period. In this group, eight subjects had sleep apnea and six had severe sleep apnea. In the next 4-year period, there were 14 new strokes; five of these patients had moderate sleep apnea and four had severe sleep apnea.

The researchers found no increased risk of stroke in subjects with mild sleep apnea.

One of the reasons that obstructive sleep apnea may increase the risk of stroke is that it has been shown to cause high blood pressure, which is a common risk factor for stroke, he explained.

Another possible reason is that when a person stops breathing, the lack of oxygen may create a reaction that makes the blood more likely to clot, he said.

Dr. Bradley suggested that further research needs to determine whether individuals with sleep apnea should be given anti-clotting therapy in addition to continuous positive airway pressure. "This is an issue that needs further research," he said.

"These findings provide strong evidence that obstructive sleep apnea is an independent risk factor for stroke," he said.


[Presentation title: Prospective Evaluation of the Relationship between Obstructive Sleep Apnea and Stroke Incidence. Abstract B88]

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