People with restless legs syndrome (RLS) are twice as likely to have a stroke or heart disease and the risk is greatest in those with the most frequent and severe symptoms, researchers say.

Most people with RLS have as many as 200 to 300 periodic leg movements per night of sleep.

These leg movements are associated with substantial acute increases in both blood pressure and heart rate.

Over the long term, RLS produces cardiovascular or cerebrovascular disease, according to research published in the Jan. 1 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.

The study found people with RLS were more than twice as likely to have cardiovascular disease or cerebrovascular disease.

"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 Dr. John W. Winkelman of the Harvard Medical School in Boston.