LOS ANGELES, CA (Catholic Online) - Those sunscreens and lotions that everyone says to use to beat melanoma? It turns out that using sun creams or covering up to avoid the sun could lessen the protective effects.

In younger women who have heeded the calls to protect themselves from the harmful effects of the sun, the effect of UVB exposure was less evident.

An autoimmune disease that causes inflammation in joints, the main symptoms of rheumatoid arthritis is joint pain and swelling.
 
There are an estimated 300,000 sufferers in the U.K. with women three times more likely to suffer from the disease than men.

The U.S. Nurses' Health Study is the first published research that tracked the health of more than 120,000 nurses since 1976, when they were aged between 30 and 55, until 2008. The second phase tracked the health of a further 115,500 nurses since 1989, when they were aged between 25 and 42, until 2009.

Researchers used UV-B flux, which is a composite measure of UVB radiation, based on latitude, altitude and cloud cover for the study.

Exposure was then estimated according to where they lived in the U.S. and ranged from an annual average of 93 in Alaska and Oregon, to 196 in such sunny states as Hawaii and Arizona. Likely estimates of UV exposure at birth and by the age of 15 were also included.

Over the period, 1,314 women developed rheumatoid arthritis. Among the nurses in the first phase, higher cumulative exposure to UVB was associated with a reduced risk of developing the disease.

Those with the highest levels of exposure were a fifth less likely to develop rheumatoid arthritis than those with the least.

Confirming other studies, this proved a link between geography and the risk of rheumatoid arthritis as well as other autoimmune conditions, including type 1 diabetes, inflammatory bowel disease, and multiple sclerosis.

No such association for UV-B exposure was found among women in the second phase because these women were younger than those in the first study.

"Differences in sun protective behaviors, for example greater use of sun block in younger generations, may explain the disparate results," the study's authors added.

"Our study adds to the growing evidence that exposure to UV-B light is associated with decreased risk of rheumatoid arthritis. The mechanisms are not yet understood, but could be mediated by the coetaneous production of vitamin D and attenuated by use of sunscreen or sun avoidant behavior."

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