May 28, 2010 -- Rheumatoid arthritis (RA) is on the rise among women after decades of decline, according to a new study, and environmental factors -- including birth control pills with lower doses of protective estrogen -- may help explain the increase.
"It's a small increase," says researcher Sherine Gabriel, MD, the William J. and Charles H. Mayo Professor of Epidemiology and Medicine at the Mayo Clinic in Rochester, Minn. "But the reason it's important is that we and many others have been documenting a systematic decline in the incidence of rheumatoid arthritis for several decades."
Because the sudden increase follows decades of decline, it's too short a time period to suspect genetic factors, Gabriel tells WebMD. She speculates it's due to environmental factors, including changes in birth control pill formulations and slower declines among women in cigarette quit rates.
About 1.3 million Americans have RA, according to the Arthritis Foundation. It occurs when the immune system mistakenly attacks the thin membrane lining the joints, called the synovium, resulting in pain, inflammation, joint damage, and potential disability.
When the increase found by the Minnesota researchers is applied to the entire U.S. population, an estimated 1.5 million U.S. adults are now affected by RA.
The study is published in Arthritis & Rheumatism.
Tracking Rheumatoid Arthritis
Gabriel and her co-researchers expanded on previous research from 1955 to 1994 by the Mayo Clinic, looking at the years 1995 to 2007. In the current study, they focused on the medical records of 1,761 residents of Olmsted County, Minn., who were age 18 or older and who had received one or more diagnoses of arthritis, not counting osteoarthritis, the wear-and-tear form that comes with age.
The researchers found that a diagnosis of RA was given to 466 patients whose average age was 55.6. Most (69%) were women.
The incidence of RA increased in women but decreased very slightly for men. For women, the incidence of RA increased by 2.5% per year from 1995 to 2007, while a decrease of 0.5% per year was seen in men.
Applied to the population, Gabriel says, that would mean at least 1.5 million U.S. adults now have RA, up from the 1.3 million.
Explaining the Increase in RA in Women
Gabriel's team can't explain the rise, but suspect a variety of environmental factors, including:
- Lower-dose birth control pills, increasingly used in favor of those with higher estrogen levels found to reduce the risk of RA. "The higher-dose estrogen pills that were used early on had more of a protective effect," Gabriel tells WebMD. As the dose declined, with the same contraceptive benefit, the pills provided less protection from RA, she says. "There actually is hard data on that."
- Cigarette smoking, which is termed by Gabriel ''perhaps the strongest environmental risk factor" for RA. Smoking rates in general have declined in the U.S., but ''women have stopped smoking at a lower rate," she says, compared with men.
- Vitamin D deficiency. Some research has suggested a link, and vitamin D deficiency has been found to be increasing, especially in women. Infections, obesity, immunizations, and socioeconomic status may be other factors explaining the rise in RA in women.
The findings are not cause for alarm for women, says Daniel Arkfeld, MD, associate professor of clinical medicine at the University of Southern California Keck School of Medicine, Los Angeles, who reviewed the findings for WebMD.
But the finding of a slight rise in RA among women will undoubtedly be news to some doctors, he says. "It's a mild trend [the increase] but it's going to be surprising to rheumatologists."
The good news, he says, is that "we're getting very good at treating it." New disease-modifying drugs have been approved recently, with the array of choices much broader than before.
As for the environmental factors behind the rise, he says some sound more plausible than others. Vitamin D deficiency, for instance, appears vary common, and all its effects are not yet known. ''We did a study and found that 50% of our patients had vitamin D deficiency, '' Arkfeld says, "and that's in sunny Southern California."
''This is an important study, although it has its limitations," says Patience White, MD, vice president of public health for the Arthritis Foundation, who reviewed the study for WebMD.
The study is relatively small, she says, and relies on medical histories of residents of one county in Minnesota, not as ethnically diverse as some other parts of the country.
Of the increase itself, she says that "a 2% increase over each year is not a lot."
"The significance here is it was a falling rate [previously] and now it's an increasing rate [in women.]"
The take-home for consumers, she says, is to get medical help when RA is suspected. Symptoms may include stiff joints, swelling and pain.
''As opposed to 10 years ago, we now have fantastic treatments that can decrease the disability and destruction of the disease," White says.