People with restless legs syndrome (RLS) are twice as likely to have a stroke or heart disease compared to people without RLS, and the risk is greatest in those with the most frequent and severe symptoms.

That's according to research published in the January 1, 2008, issue of Neurology, the medical journal of the American Academy of Neurology.

The study, the largest of its kind enrolling both men and women, involved 3,433 people with an average age of 68 who were enrolled in the Sleep Heart Health Study.

Participants were diagnosed with RLS by detailed questionnaire and asked if they had been diagnosed with a variety of systemic diseases including cardiovascular disease and cerebrovascular disease. Of the participants, nearly seven percent of women and three percent of men had RLS.

The study found people with RLS were more than twice as likely to have cardiovascular disease or cerebrovascular disease. The results remained the same after adjusting for age, sex, race, body mass index, diabetes, high blood pressure, high blood pressure medication, HDL/LDL cholesterol levels, and smoking.

"The association of RLS with heart disease and stroke was strongest in those people who had RLS symptoms at least 16 times per month," said study author John W. Winkelman, MD, PhD, with Harvard Medical School in Boston. "There was also an increased risk among people who said their RLS symptoms were severe compared to those with less bothersome symptoms."

Winkelman says although this study does not show that RLS causes cardiovascular and cerebrovascular disease, a number of potential mechanics for such a process exist.

In particular, most people with RLS have as many as 200 to 300 periodic leg movements per night of sleep and these leg movements are associated with substantial acute increases in both blood pressure and heart rate, which may, over the long term, produce cardiovascular or cerebrovascular disease.

Winkelman says there are limitations to the study, including that the diagnosis of RLS was self-reported by questionnaire rather than by clinical interview.