People with restless legs syndrome face twice the risk of a stroke or heart disease compared to people who don't have the neurological condition, a new study suggests.
The risk is greatest in people with the most frequent and the most severe symptoms of restless legs syndrome.
"This shows that restless legs syndrome has salience beyond just symptoms," said Dr David Rye, a professor of neurology at Emory University School of Medicine in Atlanta. "It's really saying, this disorder is salient, you need to recognise it."
Read: 23% of people have restless legs
Other experts added a cautionary note to the study's findings.
"This study is very well done, and the conclusions of the study are very measured.
In other words, the authors acknowledge that they can't prove that what they're studying actually causes strokes or heart attacks," said Dr Paul Greene, associate attending physician in the department of neurology at New York-Presbyterian Hospital/Columbia University Medical Center in New York City.
"They also could have picked up people with other syndromes, neuropathies and things that could influence strokes and heart attacks. There are a lot of ways in which this study could be misleading.
"They will have to do something to follow up on this before pushing a panic button," he added.
Link between RLS and heart problems
Restless legs syndrome (RLS) is a neurological disorder characterised by restlessness and a need to move the legs. Symptoms start or become worse when you are resting.
The symptoms occur mainly at night and can interfere with sleep. Some 5 percent to 10 percent of the adult population suffers from the syndrome, according to the study.
Earlier studies showed an association between restless legs syndrome and cardiovascular disease, but the studies had limitations. RLS has also suffered from a public image problem, which may explain why so few studies have explored the condition.
Read: Restless leg syndrome
"RLS has borne the brunt of a lot of skepticism," Rye explained. " snoring started out the same way... It took decades to convince primary-care physicians that we have to treat sleep apnoea, that it's not just a nuisance that dad snores. It (sleep apnoea) has a huge added risk for obesity and stroke and hypertension and cardiovascular disease."
The new study, the largest of its kind, looked at 3,433 men and women, with an average age of 68, who were enrolled in the Sleep Heart Health Study, which was originally designed to look at the cardiovascular consequences of sleep-disordered breathing.
A diagnosis of restless legs syndrome was based on a questionnaire completed by all study participants. The participants also answered questions about cardiovascular disease and stroke. Almost 7 percent of women and 3.3 percent of men in the study had restless legs syndrome.
Read: Could dark chocolate help ease poor circulation?
People with the syndrome were more than twice as likely to have cardiovascular disease or stroke.
The association was strongest among those who had RLS symptoms a minimum of 16 times a month and among those who said their symptoms were severe.
The study can't prove a cause-and-effect relationship, but such a link could make physiological sense.
Read: keep those travel legs moving
Most people with restless legs syndrome have up to 300 periodic leg movements a night, and those movements are associated with increases in blood pressureand heart rate, the study authors said.
Also, people with RLS often also suffer from sleep deprivation, which has been associated with cardiovascular disease.
"The direct data would suggest that the disrupted sleep and arousals that occur with RLS are really what's contributing to hypertension and heightened autonomic nervous system activity, which in turns leads to cardiovascular problems," Rye said. "But this (study) can't answer that kind of question."
The next study should look to see if treatments for restless legs syndrome reduce the risk for heart disease and stroke, Rye added. "Nobody has done that, because nobody has recognised that there was a problem," he said.
Stilettos physically alter legs
What are varicose veins?
Exercise keeps leg arteries clear