The study, which was funded by the National Institutes of Health, followed more than 11,000 men who were free of erectile dysfunction (ED), diabetes, and arthritis when they were enrolled in 2002. The average age of study participants was 64.
Symptoms of restless legs syndrome and erectile dysfunction were assessed using questionnaires.
Over six years of follow-up, about 2,000 men in the study developed ED.
Even after ruling out the effects of factors known to increase the risk of erectile dysfunction, like age, smoking, obesity, antidepressant medications, and snoring, researchers found that men who had at least five episodes of restless legs syndrome each month were about 50% more likely to develop ED than men who had no symptoms of the problem.
Men with more frequent symptoms were at even higher risk.
Men who experienced more than 14 episodes of restless legs syndrome each month had a 66% greater risk of developing ED than men without the condition.
The study was presented at the 2011 annual meeting of the American Academy of Sleep Medicine and the Sleep Research Society.
A Link to Low Dopamine Levels
Restless legs syndrome is a poorly understood neurological disorder that affects up to 15% of all adults. It is characterized by unpleasant sensations like pulling or creeping that often strike at night, when muscles are relaxed. These sensations typically compel sufferers to move to relieve their discomfort.
A previous study, published in 2010 by the same team, found a strong relationship between restless legs syndrome and ED in a large sample of older men.
But because that study just looked a snapshot in time, investigators couldn’t be sure which problem came first, something that could hint at how they are related.
Study researcher Xiang Gao, MD, PhD, assistant professor of medicine at Harvard University and an associate epidemiologist at Brigham and Women’s Hospital in Boston, says he thinks that low dopamine levels may be to blame for both conditions.
“Restless legs syndrome is a well-known dopamine-related disease,” Gao says. “Dopamine is also important to maintain normal sexual function, erectile function.”
What’s more, restless legs syndrome and erectile dysfunction are more common in men with Parkinson’s disease, which is caused by the death of dopamine-producing cells in the brain.
If further research confirms the findings, Gao says the studies may help doctors better screen men who might be at risk.
The research may also point to other kinds of treatment for ED.
Studies show that about 12% of the men who try medications for ED don’t get enough help from these kinds of drugs.
“There are some small studies using dopamine agonists to treat Parkinson’s disease and their ED improves,” Gao says.
This study was presented at a medical conference. The findings should be considered preliminary because they have not yet undergone the "peer review" process, in which outside experts scrutinize the data prior to publication in a medical journal.