Sun may prevent rheumatoid arthritis in women

Sunnier climates may reduce the risk of rheumatoid arthritis, according to a large US study. About 100,000 women were tracked from 1976 and another 100,000 from 1989. Their health was compared with the levels of UV-B radiation they were exposed to (based on where they lived) and the results published in the Annals of the Rheumatic Diseases.

In the 1976 group, women from the sunniest areas of the US were 21% less likely to develop rheumatoid arthritis than those living in the least sunny places.

“Our study adds to the growing evidence that exposure to UV-B light is associated with decreased risk of rheumatoid arthritis,” says Dr Elizabeth Arkema who led the study.

The positive outcomes of UVB exposure was seen in the group of older women more than the younger women, perhaps because younger women protect themselves with sunscreen.

Vitamin D is produced when UV radiation hits the skin and this could impact on the risk of developing rheumatoid arthritis. Low levels of vitamin D are involved in other immune system disorders such as multiple sclerosis and type 1 diabetes.

Another study published in 2010 found that women living in northeastern states in the US are more likely to develop rheumatoid arthritis.

“Our study adds to the growing evidence that exposure to UV-B light is associated with decreased risk of rheumatoid arthritis,” say the researchers involved in the current work. “The mechanisms are not yet understood, but could be mediated by the cutaneous production of vitamin D and attenuated by use of sunscreen or sun avoidant behaviour.”

Dr Chris Deighton from the British Society for Rheumatology comments that the sun also increases the risk of skin cancer:

“We cannot advocate everybody sitting in the sunshine all day to protect from rheumatoid arthritis, because UV-B burns people and increases the risk of skin cancer,” he says.