Dr. Symmons and her fellow panelists spoke about four phases of RA that each person moves through: Genetic risk, autoimmunity but asymptomatic, early symptoms of articular disease and active disease with synovitis.
RA Rising & Falling
To learn more about RA incidence rates and the identification of potential triggers and protective factors, researchers glean data collected from large studies, such as the Rochester Epidemiology Project at the Mayo Clinic, the Karolinska Institute of Sweden’s Epidemiological Investigation of Rheumatoid Arthritis (EIRA) and Harvard Medical School Channing Laboratory’s Nurses’ Health Study, said Dr. Symmons. These extensive, long-term data show intriguing trends in RA that help focus future research in the right directions.
Although RA is more common in women, men’s risk rises with aging, said Dr. Symmons. The Mayo Clinic data show that “the incidence of RA fell progressively in men and women between around 1955 and 1995.2 It started to rise again from 1995 to 2005. We don’t know yet what happened in the next decade,” she said.
Clues for the rise or fall in RA cases may be in well-known triggers. Some of these triggers are modifiable, such as smoking, obesity, diet and exposure to reproductive hormones. Other factors, such as aging or gender, are not modifiable, and some people may be exposed to environmental triggers, such as silica particles in the air or secondhand smoke, with little ability to control it.
Pregnancy hormones are a potential risk factor for developing RA, so the availability of oral hormonal contraceptives in the U.S. from the 1960s onward may have affected RA incidence rates in women. In addition, the hormonal concentration of oral birth control pills was higher in the 1960s than in later decades, which may have affected users’ RA risk, according to the Mayo Clinic data.
“One reason for the fall may be the protective effect of the pill in women. It was also felt that this was part of a natural change in disease incidence,” Dr. Symmons said. “No one really knows why. Some of the rise since 1995 may be due to increased prevalence of obesity, which is an environmental risk factor.”
Scientists stumbled on the pill’s potentially protective aspect in RA by accident, said Dr. Symmons. The Royal College of General Practitioners Oral Contraception Study, which collected data on 46,112 women over 39 years, looked into the health impact of the widely used medicine.3 One of the findings showed that RA risk was less than half in those who took the pill compared with those who had never taken it, she said. But researchers still aren’t sure exactly why these hormones offer this protection.
