A study in the Jan. 1 issue of the journal Sleep shows that erectile dysfunction was more common in older men with restless leg syndrome (RLS) than in those without RLS, and the magnitude of this association increased with a higher frequency of RLS symptoms.

Results show that erectile dysfunction was 16 percent more likely in men with RLS symptoms that occur five to 14 times per month (odds ratio of 1.16) and 78 percent more likely in men whose RLS symptoms occur 15 or more times a month (OR=1.78). The associations were independent of age, body mass index, use of antidepressants, anxiety and other possible risk factors for RLS. Fifty-three percent of RLS patients and 40 percent of participants without RLS reported having erectile dysfunction, which was defined as a poor or very poor ability to have and maintain an erection sufficient for intercourse.

The results suggest it is likely that the two disorders share common mechanisms, said lead author Xiang Gao, MD, PhD, instructor at Harvard Medical School, associate epidemiologist at Brigham and Women's Hospital and research scientist at the Harvard School of public health in Boston, Mass.

"The mechanisms underlying the association between RLS and erectile dysfunction could be caused by hypofunctioning of dopamine in the central nervous system, which is associated with both conditions," said Gao.

Data were collected from 23,119 men who participated in the Health Professionals Follow-up study, a large ongoing U.S. cohort of male dentists, optometrists, osteopaths, podiatrists, pharmacists and veterinarians. Participants were between the ages of 56 and 91 years, with a mean age of 69 years. To reduce possible misclassification of RLS, participants with diabetes and arthritis were excluded.

Participants were questioned in 2002 about RLS diagnosis and severity based on the International RLS study group criteria. RLS was defined as having unpleasant leg sensations combined with restlessness and an urge to move; with symptoms appearing only at rest, improving with movement, worsening in the evening or at night compared with the morning, and occurring five or more times per month.

About four percent of participants had RLS (944 of 23,119 men), and about 41 percent (9,433 men) had erectile dysfunction. Men with RLS were older and were more likely to be Caucasian. The prevalence of erectile dysfunction also increased with age.

The authors noted that the association between RLS and erectile dysfunction also could be related in part to other sleep disorders that co-occur with RLS. For example, obstructive sleep apnea and sleep deprivation may decrease circulating testosterone levels.

They also pointed out that the cross-sectional design of the study did not allow for a determination of causality. Further epidemiological studies are needed to clarify the relationship between the RLS and erectile dysfunction and to explore the biological mechanisms underlying the association.