Women living in the northeastern United States are more likely to develop rheumatoid
arthritis (RA), suggesting a link between the autoimmune disease and vitamin D deficiency,
says a new study led by a Boston University School of Public Health researcher.
In the paper, which appears online in the journal Environmental Health Perspectives, a spatial
analysis led by Dr. Vernica Vieira, MS, DSc, associate professor of environmental health,
found that women in states like Vermont, New Hampshire and southern Maine were more
likely to report being diagnosed with RA.
"There's higher risk in the northern latitudes," Dr. Vieira said. "This might be related to the
fact that there's less sunlight in these areas, which results in a vitamin D deficiency."
The study looked at data from the Nurses' Health Study, a long-term cohort study of U.S.
female nurses. Looking at the residential addresses, health outcomes and behavioral risk
factors for participants between 1988 and 2002, researchers based their findings on 461
women who had RA, compared to a large control group of 9,220.
RA is a chronic inflammatory disease that affects the lining of the joints, mostly in the hands
and knees. This chronic arthritis is characterized by swelling and redness and can wear down
the cartilage between bones. RA is two to three times more common in women than in men.
Although the cause of RA is unknown, the researchers wrote, earlier studies have shown thatvitamin D deficiency, which can be caused by a lack of sunlight, has already been associatedwith a variety of other autoimmune diseases."A geographic association with northern latitudes has also been observed for multiple sclerosisand Crohn's disease, other autoimmune diseases that may be mediated by reduced vitamin Dfrom decreased solar exposure and the immune effects of vitamin D deficiency," the authorswrote.The authors said further research is needed to look into the relationship between vitamin Dexposure and RA.Dr. Vieira said she and her co-authors were somewhat surprised by the findings. A previousgeographic study of RA had suggested an ecologic association with air pollution, she said."The results were unexpected," Dr. Vieira said. "Prior to the analysis, we were more interestedin the relationship with air pollution. I hadn't given latitudes much thought."In addition to the geographic variation, the study suggested that the timing of residency mayinfluence RA risk. "Slightly higher odds ratios were observed for the 1988 analysis suggestingthat long term exposure may be more important than recent exposure," the study said.Dr. Vieira and other BUSPH researchers previously have used innovative spatial-temporalanalyses to study the incidence of breast cancer, specifically focused on Cape Cod.
