Why the incidence of RA in women is increasing, but not in men?
The Mayo Clinic also did research as to why it seems to be increasing in women. The incidence and prevalence of RA vary widely across populations, geographic areas, and time periods, probably as a result of an interplay between genes and environment. One factor that has been considered, and the strongest, is cigarette smoking.
While smoking overall has declined in recent years, the decline has been much slower among women. The percentage of men who smoked fell from 78% in the earlier decade to 59% whereas rates of smoking among women remained almost unchanged.
Another factor is Vitamin D deficiency. Which seems to also be rising among women in recent decades, may further contribute, along with other environmental factors such as infections, obesity, and socioeconomic factors.
Estrogen, the hormone, has played a part in RA. More women develop RA during the months after childbirth, or during the pre-menopause years. A study was done about this in 2003, you can read about it HERE. It stated that, irregular menstrual cycles correlated with an increased risk of RA. And women who breastfed longer than twelve months were less likely to develop Rheumatoid Arthritis.
Also in the study it stated that certain infections could have played a role in the increase of RA. An infection called Porphyromonas gingivalis, a gram-negative organism associated with periodontists. It stated that this bacteria could mediate changes in the body resulting in expression of RA-specific autoantibodies.
UPDATE: Here is an email from my Rheumatologist responding to this very question:
Thanks for your email.
The short answer to your question is that we don't know.
Women are more frequently affected not only by RA but also by lupus erythematodes (SLE) and other rheumatic diseases. Differences in sex hormone levels are the most commonly cited reason. In line with this, RA often gets better during pregnancy (which is characterized by drastically changed hormone levels). In contrast, SLE tends to get worse during pregnancy (these things are complicated).
Women have two X chromosome while man have an X and a Y chromosome. It could also be that genes located on the X or Y chromosome increase (or decrease) the risk for getting the disease. And then there are other possible factors such as differences in environmental exposures, eating habits, etc... So the long answer is that there are hypotheses but no conclusive explanation.
Sadly, it seems that more research needs to be done as to why it is increasing in women, and not in men. Nothing seems to be definite. In the study they basically said to not smoke, and to get checked for Vitamin D deficiency, which is only great if you don't already have RA. My advice to those who don't have RA yet, don't smoke, and make sure you have enough Vitamin D and Calcium in your diet. Drinking milk, eating yogurt and sunlight are three examples of Vitamin D. They also sell Vitamin D (with calcium) supplements and your local vitamin stores. However, even doing that doesn't seem to necessarily help. I've had JRA since I was 3, never smoked a day in my life and have always been a big milk drinker/yogurt eater and I take 2 Vitamin D pills a day. Scientists are doing what they can, but are more concerned about finding a cure for RA, which in my book is excellent. In meantime, us women need to stay strong and stick together, because we are strong, wonderful women who don't need an illness to let us down!