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NEW YORK (Reuters Health) - Two disorders that seem completely unrelated except that each is the focus of massive drug company ad campaigns may actually have something in common: Older men who suffer from restless legs syndrome at night are almost twice as likely to have erectile dysfunction as those without restless legs, researchers report.
Dr. Xiang Gao, of the Harvard School of Public Health, Boston, and his colleagues studied more than 23,000 male dentists, optometrists, veterinarians and other health professionals, who would complete health-related surveys at regular intervals.
In 2000 and 2004, the men were asked to rate their erections on a five point scale from very poor to very good. In 2002, the men answered questions related to restless legs syndrome symptoms. None of these men had diabetes or arthritis, which can both increase the risk of restless legs.
About four percent -- 944 -- of the men reported symptoms of restless legs syndrome. These men had an average age of 70, while those without restless legs were on average about two years younger, tended to exercise more, and were less likely to smoke.
Of those who reported restless legs, more than half -- 53 percent - also reported trouble with their erections, compared to 40 percent of those who did not complain about restless legs.
The likelihood of erectile dysfunction also varied with the severity of restless legs symptoms, researchers found. Men who had restless legs 5 to 14 nights per month were 16 percent more likely to have erectile dysfunction compared to men without restless legs, while men with more than 15 nights of restless legs symptoms had a 78 percent higher chance of erectile dysfunction.
Neither age, ethnicity, obesity, nor tobacco use had any significant effect on the likelihood of the link between the two conditions.
The survey did not ask volunteers if a doctor had diagnosed either of the disorders, only about related symptoms, which is a weakness, said Dr. Thomas Pollmächer, the director of mental health at Ingolstadt Hospital, Germany.
"The problem with the study is the very rough assessment for restless legs syndrome," Pollmächer told Reuters Health, meaning that other conditions could be confused with restless legs. Pollmächer has studied the syndrome in pregnant women.
Dr. Clete Kushida, president of the American Academy of Sleep Medicine, which publishes the journal Sleep, told Reuters Health the study relies on sound reasoning and is generally well done. However, echoing Pollmächer's critique, he notes that the criteria of restless legs syndrome changed after the 2002 survey, which could affect how meaningful the results are.
"It would have been nice to have had the exact four criteria used," Kushida said. Those criteria are an urge to move the legs, getting temporary relief with movement, worse symptoms at rest, and worse symptoms in the evening.
Gao agreed that the diagnosis of restless legs syndrome is not as straightforward as other diagnoses, and that some of the men who reported restless legs syndrome probably did not really have it.
That lack of clarity has led some to suggest that restless legs syndrome is an example of "disease mongering," in which drug companies expand the definitions of a disease to make it seem that more people need to be treated. Boosted by a widespread ad campaign, sales of Requip, one of the two FDA-approved treatments for restless legs syndrome, reached more than $500 million before the agency approved a generic form of the drug in 2008.
It wasn't the ads that prompted Gao to undertake this work, and no drug companies were involved in the federally-funded study. Gao told Reuters Health that his team had noticed that both conditions seem to involve dopamine, an important message-carrying chemical, or neurotransmitter.
He'd like to do a study with men who have confirmed restless legs syndrome to better test the potential link.
Still, Kushida said, "based on these findings, it would be a good idea for doctors to ask their male restless legs patients if they have erectile dysfunction."
Kushida suggested that there may be a role for restless legs drugs in erectile dysfunction treatment, and said the question warrants further research.
SOURCE: Sleep, January 2010.