An estimated 12 million Americans -- including half a million children -- are affected by the disorder, which causes a "creeping, itching, pulling, creepy-crawly, tugging, or gnawing" sensation in the limbs, according to the Restless Legs Foundation.
"My legs felt like they were being shocked and they would practically move on their own," said Kathy Page of Sedalia, Mo., who suffers from the condition.
"It is hard to explain the immense need to move your legs," she told ABCNews.com. "It's a feeling that if you don't move them and move them now you will just go insane."
"It's a very real condition," said Georgianna Bell, RLS Foundation executive director. "It's something you must have a prescription for -- not just something you pick up over the counter."
Researchers at Harvard University School of Public Health took surveys of 88,000 men and women and found that those who were generally obese -- with a body mass index higher than 30 -- were at 40 percent higher risk of developing restless legs syndrome.
Thick Waists Cause Greater Risk
But those with a high waist circumference had an even higher risk -- 60 percent, according to the study that was published in the April issue of "Neurology," the medical journal of the American Academy of Neurology.
Scientists think that the levels of dopamine -- which control both movement and the pleasurable feeling from eating -- may be involved.
Restless legs syndrome affects about 5 percent to 10 percent of the general population, affecting sufferers' work, relationships and health. At its worst, the syndrome can cause anxiety and depression, according to sleep experts.
Often symptoms are worse at night or when resting and resolve upon moving. RLS can also cause difficulties falling or staying asleep. Many also have periodic leg movements -- jerks that occur every 20 or 30 seconds throughout the night.
According to the Harvard study, the higher risks seem to lie in lower levels of dopamine, the chemical in the brain that transmits signals between nerve cells and controls movement.
Though scientists don't exactly know why, lower dopamine levels are associated with Parkinson's disease, as well as restless legs syndrome.
Obese at Risk for RLS
Dr. Xiang Gao, one of the co-authors of the study, says some studies suggest that obese people have lower dopamine receptor levels in the brain.
"Since decreased dopamine function is believed to play a critical role in RLS as well, this could be the link between the two," said Gao, a research associate at the department of nutrition at Harvard School of Public Health.
The study points to a "significant risk" for those who are obese, Gao told ABCNews.com, "especially with the high prevalence of obesity."
"Forty percent is significant for public health because right now 30 percent of all Americans are obese," he said.
Gao said doctors might consider weight reduction programs for patients who suffer from restless legs syndrome, though the study points out an association between the two, rather than a cause and effect.
In the study, which was supported by a grant from the National Institutes of Health and the National Institute of Neurological Disorders and Stroke, none of the participants had diabetes, arthritis or were pregnant.
Of the groups, 6.4 percent of the women and 4.1 percent of the men were identified as having RLS.
Weight Gain Noticed
Kathy Page has suffered from RLS most of her life. Though medication controls some of the symptoms, at their worst, she has a "complete inability" to lie still and relax.
"Imagine an itch on the bottom of your foot when you have socks and tightly tied shoes," said the 53-year-old. "You just can't get them off fast enough to get to the itch. Now imagine that magnified 50 times and you sort of get the idea."
Page, who lives on a farm and works as a purchasing agent for an electric cooperative, said she finds the Harvard study "interesting." She is not a diabetic or taking anti-depressives.
"I have never connected it with my weight gain, but the fact is I have gained a lot of weight," she told ABCNews.com. "I have not studied this information completely but it certainly does make one wonder if there is a connection. Obesity can cause many problems that we know."
One of the challenges related to RLS is many do not understand the disorder.
Doctors can sometimes confuse RLS with other neurological conditions like peripheral neuropathy or nocturnal cramps, according to Alon Avidan, director of the Sleep Center at the University of California Los Angeles.
In children, it can be mistaken for Attention Deficit Hyperactivity Disorder.
RLS Confounds Doctors
"Some [doctors] are not aware of the disease and some have never heard of it," Avidan told ABCNews.com. "Mainly it's lack of education how to treat it and many confuse it with other disorders. People are also afraid to commit patients to treatments that may involve long-term therapy and are not aware the drugs are quite effective."
Doctors prescribe dopamine agonists like Requip or Mirapex, which can have side effects, like daytime sleepiness, nausea and drop in blood pressure. Some patients also experience "rebound" effects, making the symptoms worse.
Avidan said the obesity connection was "new to me," although he acknowledged the importance of dopamine in RLS.
"It's not well understood why an area of the brain stops manufacturing dopamine," he said.
While some studies show embryonic cells can promote dopamine function in the brain, those therapies are not yet available to the public, according to Avidan.
"Right now the best therapy is to give chemicals they are missing," he said. "But it's not the entire puzzle."
Scientists say more research is needed to confirm whether obesity causes RLS and whether keeping a low BMI score and small waist size could help prevent the disorder.
Study Has Potential
But the study has "potential significance," according to Dr. John Winkelman, who sits on the board of the RLS Foundation and is medical director of the Sleep Health Center of Brigham and Women's Hospital in Boston.
"We already know RLS is associated with a variety of other bad outcomes," he told ABCNews.com. "Sleep disturbances increase the risk of anxiety and mood disorders."
Winkelman has published a paper on a similar association between RLS and cardiovascular disease. "But we need more longitudinal studies to help determine which way the arrow points," he said.
Neurobiologists now know that sleep problems can result not only in car and job site accidents, but can impair physical and mental health, as well.
"Our mothers always told us that sleep was important," Winkelman said. "But it's been the poor stepchild of medicine and there is not much known about it, because for a long time, it was looked at through the lens of dreaming, which is not real science.
"We are now realizing that sleep, like nutrition, is part of overall health," he said. "We spend eight hours a night sleeping and if there's no point in sleep it's the biggest mistake evolution has ever made."