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Arthritis risk 'reduced' by sunshine

5th February 2013

Researchers in the United States say that people who live in a sunnier climate could reduce their risk of developing rheumatoid arthritis (RA).

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In a study of more than 200,000 women, they suggest there is a link between the risk of getting RA and sunlight.

Writing in the journal Annals of the Rheumatic Diseases, the researchers from the Harvard Medical School speculated the vitamin D produced when sunlight falls on exposed skin, may protect the body. But the findings sparked warnings that people should not spend long hours in strong sunlight.

An often intensely painful condition, RA is caused by an attack on joint tissue by the body's own immune system. The reasons behind the auto-immune response are still unknown, but the condition is more commonly found in women.

Two groups of more than 100,000 women were followed from 1976 and 1989 respectively, and their health compared with their estimated levels of UV-B radiation exposure, based simply on their location and the hours of sunlight associated with it.

Those in the sunniest parts of the country who got the most sun were 21% less likely to develop RA, the study found. However, this link only held for the 1976 group. In the 1989 group, there was no link between UV levels and the risk of RA.

It is possible that, by the time the younger cohort enrolled in the study, warnings about using sunscreen and the risk of skin cancer had changed the women's behaviour.

The 1989 group showed no benefit from living in sunnier locations, compared with their peers in cloudier climates.

It is possible, the researchers wrote, that the protective effect is linked to higher levels of vitamin D in sunnier climates.

Other immune system disorders like multiple sclerosis have been linked to low levels of vitamin D.

However, Chris Deighton of the British Society for Rheumatology said he would not advocate everybody sitting in the sunshine all day to protect themselves from rheumatoid arthritis, because UV-B burns people and increases the risk of skin cancer.

He added that the study was interesting, and presented more clues about how environmental factors can affect a person's chance of getting RA.

He said recent years had seen greatly improved treatment options in rheumatology, but that anything that increased understanding of the crippling disease was welcome.

According to Alan Silman, medical director of Arthritis Research UK, previous studies have not shown that vitamin D is a useful treatment for rheumatoid arthritis.

He said further research was currently under way to try to determine whether vitamin D can alter the aggressive autoimmune response seen in RA, and whether this effect could be used to make it less harmful, or prevent it from happening.

He said the current advice was for people to spend up to 15 minutes in the sun during summer months with their face and arms exposed, so as to top up their vitamin D levels.

 


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