Findings reported in an article published online on March 25, 2010 in the journal Environmental Health Perspectives suggest that increased vitamin D from sunlight exposure could have a protective effect against rheumatoid arthritis (RA), a chronic autoimmune disease with unknown causes.
For the current investigation, Boston University School of Public Health associate professor of environmental health Verónica Vieira, MS, DSc and her colleagues analyzed data from the Nurses’ Health Study, which enrolled female nurses in the United States beginning in 1976. Four hundred sixty-one participants diagnosed with rheumatoid arthritis between 1988 and 2002 were compared to 9,220 control subjects who did not have the disease. The researchers examined the association between rheumatoid arthritis risk and residential address as ascertained from questionnaires completed every two years from 1988 to 2002.
The team found a higher risk of rheumatoid arthritis among women living in the northeastern United States, suggesting that less sunlight exposure, and, consequently, decreased vitamin D production, could be a factor in the development of the disease. A slightly greater risk was found for higher latitude residence in 1988 compared with the time of diagnosis, suggesting that long term exposure could be more important than recent exposure.
“There’s higher risk in the northern latitudes,” Dr Vieira stated. “This might be related to the fact that there’s less sunlight in these areas, which results in a vitamin D deficiency.”
“The results were unexpected,” she added. “Prior to the analysis, we were more interested in the relationship with air pollution. I hadn’t given latitudes much thought.”
“A geographic association with northern latitudes has also been observed for multiple sclerosis and Crohn’s disease, other autoimmune diseases that may be mediated by reduced vitamin D from decreased solar exposure and the immune effects of vitamin D deficiency,” the authors write in their discussion of the findings. “Further analysis that examines the relationship between vitamin D exposure and rheumatoid arthritis is warranted to explore these results.”