Obstructive sleep apnea in middle-aged adults may increase the risk of coronary artery disease by up to five-fold, research in Sweden suggests. However, successful treatment of the sleep apnea significantly cuts that risk.

Although evidence supports ties between sleep apnea -- that is, brief but frequent episodes during the night when breathing becomes blocked -- and coronary artery disease, a causal relationship has not been established, Dr. Yuksel Peker and his colleagues at Sahlgrenska University Hospital in Goteborg note. The concomitant presence of other illnesses further complicates the ability to delineate cause and effect.

For their study, Peker's team identified 308 middle-age individuals (ages 30 to 69 years) who had been evaluated for obstructive sleep apnea in 1991 and were free of any heart disease at baseline. Nearly one-third (n=105) patients had documented obstructive sleep apnea.

Patients were offered various standard treatments including CPAP (continuous positive airway pressure), surgery, or an oral appliance. Sleep apnea was not resolved despite treatment or offers of treatment in 65 patients.

Over the next 7 years, coronary artery disease was diagnosed in 16.2 percent of patients with sleep apnea and 5.4 percent of those without apnea. Eight deaths due to coronary artery disease occurred in the apnea group and one in the non-apnea group.

Among patients with ineffective treatment, coronary artery disease was diagnosed in 24.6 percent versus 3.9 percent of those effectively treated.

In "multivariate analysis," obstructive sleep apnea at baseline nearly quintupled the risk of developing coronary artery disease, the investigators report, regardless of age, gender, high blood pressure, diabetes, or current smoking.

However, effective sleep apnea treatment reduced the increased risk by about two thirds.

In the European Respiratory Journal, Peker's team maintains that their study "clearly suggests a causal relationship between obstructive sleep apnea and coronary artery disease."

"Even mild obstructive sleep apnea seems to have a substantial effect on coronary artery disease risk, and highly effective treatment should therefore be provided," they write.