The researchers have revealed that their study included 350 adult patients from Olmsted County, MN, whose average age was 56.5 years. The majority, 69 percent, were women.
"This is a significant finding and an indicator that more research needs to be done to better understand the causes and treatment of this devastating disease," said Sherine Gabriel, M.D., Mayo Clinic rheumatologist and lead investigator on the study.
From 1955 to 1994, the incidence of rheumatoid arthritis had continually been on the decline, which apparently changed beginning in the mid-1990s.
When Mayo researchers analyzed patient data from early 1995 to the start of 2005, they found that both the incidence and prevalence (percentage) of the condition were rising.
They found that 54 women out of every 100,000 developed rheumatoid arthritis each year in that decade, much ahead of approximately 36 women in the previous decade.
For men, the figure was 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.
Investigators are unsure of why this is happening, but they suspect an environmental factor to have a role in the shifting incidence and prevalence among women.
The study was presented at the annual meeting of the American College of Rheumatology/Association of Rheumatology Health Professionals in San Francisco.