Jan. 4, 2010 -- Older men with restless legs syndrome may have an increased risk for erectile dysfunction (ED), new research from Boston's Harvard Medical School and Brigham and Women's Hospital suggests.
Men in the study who most often experienced symptoms of restless legs syndrome (RLS) were the most likely to also report problems getting and maintaining erections.
The finding does not prove that RLS causes ED, but it raises the possibility that the two conditions share one or more common causes, study researcher Xiang Gao, MD, PhD, tells WebMD.
"This is the first study to look at this, so there is still a lot we don't know," he says, adding that the next step would be to follow older men to see if those with RLS have a higher risk for developing ED, or vice versa.
RLS, Parkinson's Disease, and ED
It is estimated that around 12 million Americans have restless legs syndrome. The numbers may be much higher, however, because the condition is believed to be both underdiagnosed and frequently misdiagnosed.
RLS is characterized by an uncontrollable urge to move the legs when at rest in an effort to relieve unpleasant sensations often described as feelings of burning, tugging, pins and needles, or the feeling that insects are crawling inside the legs.
It affects both men and women, and the most severe cases tend to occur in people who are middle-aged or older.
In an earlier analysis, Gao and colleagues reported that men with erectile dysfunction were four times as likely to develop Parkinson's disease over 16 years of follow-up as men without ED.
Because Parkinson's and restless legs syndrome are both neurological movement disorders, the researchers decided to study RLS and ED.
The analysis included more than 23,000 men enrolled in the Health Professionals Follow-up study, which is a large, ongoing study of male dentists, optometrists, osteopaths, podiatrists, pharmacists, and veterinarians.
In a 2002 survey, about 4% of the men reported having a diagnosis of RLS and 41% reported having erectile dysfunction.
Not surprisingly, the prevalence of both RLS and ED increased with age.
The Role of Dopamine
Men with RLS who had five to 14 restless leg episodes a month were 16% more likely to report ED than men without RLS; men with 15 or more RLS-related episodes a month were 78% more likely to report having problems getting or maintaining an erection.
The study appears in the January issue of the American Academy of Sleep Medicine journal Sleep.
If RLS and ED are related, the chemical dopamine, which helps regulate both movement and mood, may be the common link.
A shortage of natural dopamine in the brain is believed to play a role in Parkinson's disease and restless legs syndrome; drugs that activate brain receptors that produce dopamine are used to treat both conditions.
Low dopamine levels are also thought to be a contributing factor in erectile dysfunction.
Another potential explanation for the observed association may be lack of sleep.
People with RLS commonly experience sleep deprivation due to their involuntary nighttime limb movements, and sleep deprivation is known to decrease circulating testosterone levels, which can lead to ED.
"Anything that disrupts sleep can cause ED," says David Schulman, MD, MPH, who directs the Emory Sleep Disorders Laboratory in Atlanta. "I don't think it is possible in a study like this one to adjust for that."
Schulman says more study is needed to determine if restless legs syndrome and erectile dysfunction share a common cause.
"I don't look at this as something that will change the way I or anyone else practices medicine right now," he says.