"RLS affects five to 10 percent of adults across the country," said study author Xiang Gao, MD, PhD, with Harvard School of Public Health, Harvard Medical School and the Channing division of network medicine, Brigham & Women's Hospital in Boston. Gao is also a member of the American Academy of Neurology. "Our study highlights the importance of recognizing this common but underdiagnosed disease."

For the study, 18,425 men with an average age of 67 who did not have diabetes, arthritis or kidney failure were evaluated for RLS. A total of 690 of the men, or 3.7 percent, met the criteria for restless legs syndrome at the beginning of the study. Information about major chronic diseases was collected every two years. During the eight years of study follow-up, 2,765 of the participants died. Of the people with RLS, 171, or 25 percent, died during the study, compared to 2,594, or 15 percent, of those who did not have RLS.

The study found that men with RLS had a nearly 40 percent increased risk of death compared to men without RLS. The association dropped only slightly after adjusting for factors such as body mass index, lifestyle, chronic conditions, lack of sleep and other sleep disorders. When the researchers excluded people with major chronic conditions such as cancer, heart disease and high blood pressure from the analysis, the association between RLS and an increased risk of death rose to 92 percent higher than those without RLS.

"We found that the increased risk was not associated with the usual known risk factors, such as older age, being overweight, lack of sleep, smoking, being physically inactive and having an unhealthy diet," Gao said. "The increased mortality in RLS was more frequently associated with respiratory disease, endocrine disease, nutritional/metabolic disease and immunological disorders. Through research, we need to pinpoint why and how RLS leads to this possible higher risk of dying early."

Although RLS can occur in children, the study did not assess whether there was a long-term risk in this population.

The study was supported by the National Institutes of Health and the National Institute of Neurological Disorders and Stroke.