Aug. 6 (HealthDay News) -- The sun's ultraviolet (UV) rays may trigger certain types of autoimmune diseases in women, a new study has found.

"This study found that women who lived in areas with higher levels of UV exposure when they developed an autoimmune muscle disease called myositis were more likely to develop the form known as dermatomyositis, which weakens the muscles and causes distinctive rashes, instead of the form called polymyositis that does not have a rash," Dr. Frederick W. Miller, chief of the Environmental Autoimmunity Group at the National Institute of Environmental Health Sciences, said in a news release.

"Although we have not shown a direct cause-and-effect link between UV exposure and this particular autoimmune disease, this study confirms the association between UV levels and the frequency of dermatomyositis that we found in a previous investigation," he continued.

For the study, the researchers analyzed the autoantibodies of 380 patients who'd been diagnosed with dermatomyositis or polymositis.

"Patients with autoimmune diseases make a variety of autoantibodies that are unique to different conditions," Miller explained. "One autoantibody specifically associated with dermatomyositis is called the anti-Mi-2 autoantibody and we know from our previous research that UV radiation increases levels of the Mi-2 protein that this autoantibody binds to."

In addition to finding that women with higher UV exposure levels were more likely to develop dermatomyositis, the researchers also found an association between UV levels and the percentage of women with the anti-Mi-2 autoantibody.

"More research is clearly needed to understand the potential links between UV radiation and the development of autoimmune diseases and autoantibodies in women," Miller said in the news release.

The study appears in the August issue of the journal Arthritis & Rheumatism.

SOURCE: U.S. National Institute of Environmental Health Sciences, news release, July 30, 2009