Last week at the American College of Rheumatology annual meeting, researchers from the Mayo Clinic presented new data finding that from 1995-2005 the incidence and prevalence of rheumatoid arthritis rose in women after having declined from the mid-1950's through the mid 1990's.
Since 1995, the incidence has risen from 36 women out of every 100,000 that developed rheumatoid arthritis each year, to 54 women of every 100,000. Interestingly, the incidence for men remained at about 29 per 100,000. Overall, the percentage of the entire population with the condition rose from 0.85 percent to 0.95 percent.
The researchers did not have a clear reason for the trend, but stated that an environmental factor may have a role. It should be noted that this was a relatively small study, which included 350 adult patients from Olmsted County, MN. The majority, 69 percent, were women.
Scientists have generally believed that development of RA is linked to both genetic and environmental factors and the interaction between them. For example, smoking has been found to be a significant risk factor for seropositive RA, so people with a genetic predisposition to develop seropositive RA are even more likely to develop it if they smoke. Other environmental factors that have been associated with RA include hormone use, exposure to occupational silica, mineral oil. It has also been suggested that regional climate differences, soil composition, UV light, exposure to infectious diseases, socioeconomic factors and differences in diet and exercise (lifestyle difference) may all play roles.
So is there something particular about Olmstead County, MN, which includes the city of Rochester, that is causing this trend? Could it be that more people there are smoking, or possibly changes in the air or water quality or other lifestyle or other demographic factors? Or are other cities and counties like it also experiencing an increase? I think it would be interesting to expand the study to populations across Minnesota and the country to determine whether the incidence and prevalence are rising across the country or just in certain parts of the country. Perhaps it would lead to further studies in the places where incidence is rising to look specifically at environmental factors. It would also be interesting to compare this and other studies discussing environmental factors and geographic variation in the incidence of RA. For example, international studies have found that RA is more common in Northern Europe and North America than Southern Europe, Africa and developing countries.
Additionally, a recent study published in the August issue of the Archives of Internal Medicine, theorized that there may be a potential ecological association between living in states with higher air pollution and the risk of developing RA, because the data found that women living in more polluted industrial regions (general New England and the Midwest) had a greater risk of RA. This study analyzed data from over 83,000 female participants over decades by region of the country at birth, age 15 and age 30. The study grouped the states into the geographic areas of New England, the Mid-Atlantic, Midwest, Southeast and Southwest and West. In short, the researchers found that women in New England and the Midwest, which have historically has higher levels of industrial air pollution, were 37-45% more likely to develop RA than women in the West (pacific and mountain regions). They also found that women in the West were less likely to be smokers, had lower exposure to cigarette smoke at work and had a higher mean age for developing RA and were less likely to have a positive rheumatoid factor than women in the Eastern part of the U.S. So if Minnesota is considered a Midwestern state, could air pollution then be a significant factor in the May Clinic's recent findings?