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Genetics unquestionably play a key role in, but do not adequately explain, the variability in incidence and prevalence of rheumatoid arthritis (RA). In the last 30 years, incidence of RA was thought to be falling. To evaluate recent trends, Mayo Clinic researchers reviewed the incidence and prevalence of RA in Olmsted County, Minnesota, from 1995 through 2007.
The investigators found a modest increase in the incidence and prevalence of RA during this period in women, but not in men; they entertained numerous hypotheses to explain this finding. Implicated were a slower decline of cigarette smoking among women, a greater incidence of vitamin D deficiency, and the switch in recent decades to oral contraceptives that contain lower doses of estro…