MONDAY, April 6 (HealthDay News) -- Having a big belly or being obese appears to increase the risk for restless legs syndrome (RLS), a new study finds.

Some 5 percent to 10 percent of adults in the United States have RLS, a disorder that causes people to feel a compelling need to move their legs, especially when they're lying down. The condition can have a substantial impact on sleep, daily activities and quality of life, researchers say.

In the new study, "we found that obesity was associated with a 40 percent higher risk of having RLS," said lead researcher Dr. Xiang Gao, an instructor in medicine at the Harvard School of Public Health. "Individuals with a higher waist circumference, a marker for central obesity, are also 60 percent more likely to having RLS relative to those with a low waist circumference," he added.

The researchers also found an association between obesity at age 20 and a higher risk of having the disorder in mid-life or later, Gao said, while noting, "This suggests that obesity could be a risk factor for development of RLS."

The report is published in the April 7 issue of Neurology.

For the study, Gao's team collected data on almost 89,000 men and women who took part in either the Health Professionals Follow-Up Study or the Nurses' Health Study II. Among these people, 6.4 percent of women and 4.1 percent of men reported having RLS.

The researchers found that obese men and women were almost one-and-a-half times more likely to have RLS compared with their normal-weight counterparts. Moreover, those with the largest waists were also more likely to have RLS compared with people with the slimmest waists.

Some studies suggest that obese people have lower dopamine receptor levels in the brain. Since decreased dopamine is believed to play a role in RLS, there could be a link between obesity and lower dopamine levels, Gao said. Dopamine is produced by the body and transmits signals between nerve cells.

"If future prospective studies confirm that obesity is a risk factor for RLS, weight reduction may contribute to RLS prevention," Gao speculated.

Dr. Carlos Singer, director of the Center for Parkinson's Disease and Movement Disorders at the University of Miami School of Medicine, said the study may be yet another reason to watch your weight.

"This is a warning to all of us -- watch out for obesity," Singer said.

But Singer cautioned that the link between obesity and RLS remains unclear and the two conditions may simply be linked by some other, as yet unknown, factor. Still, he added, it can't hurt to try and lose weight in order to stave off RLS, since "we have plenty of good reasons already not to be obese."

The finding may also provide more clues to the origins of RLS, Singer said. The link between the condition and decreased dopamine is interesting, he added, because dopamine is also a hallmark of Parkinson's disease, another movement disorder.

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