After a sharp decline in the incidence of rheumatoid arthritis (RA) over the previous 4 decades, it appears to have increased slightly in women in more recent years, along with an increase in prevalence. The reasons are unknown, but the cumulative effect of multiple environmental factors (eg, cigarette smoking, vitamin D deficiency, infections, immunizations, obesity, and socioeconomic status) may play a role.
Myasoedova and colleagues assembled a population-based incidence cohort of persons 18 years or older who fulfilled the American College of Rheumatology 1987 criteria for the classification of RA. Overall incidence rates were age- and sex-adjusted to the population of white persons in the United States in 2000.
For the 1995-2007 period, the overall age- and sex-adjusted annual RA incidence was 40.9 per 100,000 population. The age-adjusted incidence in women was 53.1 per 100,000 population, compared with 27.7 per 100,000 in men. During that period, the incidence of RA increased moderately in women but not in men. The overall age- and sex-adjusted prevalence on January 1, 2005, was 0.72%, compared with a prevalence of 0.62% in 1995.
The authors noted that the effect of other, as yet unknown risk factors on changes in RA incidence over time cannot be excluded.
