Living in a climate with more sunshine may lower the risk of developing rheumatoid arthritis, a new US study has revealed.
The research, published in the journal Annals of the Rheumatic Diseases, suggested a link between sunlight and the risk of developing this autoimmune disease, which leads to inflammation of the joints and surrounding tissues. The condition can occur at any age and can be very painful.
The researchers suggested that vitamin D, which is produced in sunlight, may reduce the risk of developing rheumatoid arthritis. Yet experts warn that people should not sit in the sun for extended periods as they may develop skin cancer.
Rheumatoid arthritis is more common in women, but it is not known what causes it.
Researchers at Harvard Medical School monitored over 200,000 women divided into two groups. The first were followed from 1976 onwards, while the second group was monitored from 1989. Then, their health was compared with the projected levels of UV-B radiation they were exposed to on the basis of where they lived.
In the 1976 group, those living in the sunniest parts of the USA were 21% less likely to develop the disease relative to those exposed to the least UV radiation. In the younger group of women, UV levels had no effect upon the risk of rheumatoid arthritis. The researchers suggested that the lack of benefit from living in sunnier places in the 1989 group could be down to the greater use of sun block in recent years.
The US study gives more clues on how the environment can affect the odds of getting rheumatoid arthritis, said Dr Chris Deighton, president of the British Society for Rheumatology.
While we know that many people with arthritis have low vitamin D levels and this can affect the immune cells which may cause the disease, research has not proved, thus far, that the vitamin D which is produced when UV radiation hits the skin is a useful treatment for rheumatoid arthritis, said Prof Alan Silman, medical director of Arthritis Research UK, as quoted by the BBC.
The organisation is currently performing lab studies to see if vitamin D can alter the aggressive immune response found in rheumatoid arthritis and turn it into a less damaging or even a protective one, Prof Silman added.