(AP) -- The nighttime twitching of restless legs syndrome may be more than an annoyance: New research suggests that in some people, it could be a sign of hidden heart problems.
People with very frequent leg movements during sleep were more likely to have thick hearts - a condition that makes them more prone to cardiac problems, stroke and death, the study by Mayo Clinic doctors found.
"We are not saying there is a cause-and-effect relationship," just that restless legs might be a sign of heart trouble that doctors and patients should consider, said Dr. Arshad Jahangir, a heart rhythm specialist at the Mayo Clinic Arizona in Scottsdale.
He led the study and gave results Sunday at an American College of Cardiology conference in New Orleans.
Restless legs syndrome is thought to afflict millions, though there's argument about just how many. Some doctors think its seriousness has been exaggerated, possibly to help sell treatments.
The syndrome gained more scientific respect several years ago, when several genes were linked to it. And doctors have long known that other types of sleep disturbances such as sleep apnea raise the risk of heart problems.
The new research suggests the same may be true of the syndrome, famously referred to as "the jimmy legs" in an old "Seinfeld" episode.
The study is one of the first to look at how the syndrome affects health "other than the nuisance that it is," said the cardiology college's president, Dr. Ralph Brindis of the University of California, San Francisco.
It involved 584 people diagnosed with the syndrome by a neurologist based on four widely used criteria. Participants were given an imaging test that allowed heart thickness to be measured three ways, and were kept overnight so their sleep could be monitored.
Afterward, researchers divided them into two groups based on the frequency of leg twitches. The 45 percent who twitched at least 35 times per hour were more likely to have the thick-heart condition than the other 55 percent of study participants who kicked less often.
Looking at all study participants about three years later, researchers saw that those with severely thick hearts - about a quarter of the total group - were more than twice as likely to have suffered a heart problem or to have died.
The study was funded by the National Heart, Lung and Blood Institute and a private grant.
People with restless legs shouldn't panic, but it's worth talking with doctors about whether more tests are needed to look for an enlarged heart, Jahangir said.
"Don't ignore it. Discuss it with your physician," he said.
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More information: Heart meeting: http://www.acc.org