Rheumatoid arthritis (RA) is much more common in women than it is in men, so research has traditionally focused on women's health issues when looking at possible causes and treatments. A recent study published in the British Medical Journal drew on data from the Swedish Epidemiological Investigation of Rheumatoid Arthritis (EIRA) which tracked women over 18 who lived in Sweden between the years 1996 and 2014. Out of that data, women who had been diagnosed with rheumatoid arthritis were compared to women who did not have RA. Blood tests and health information were collected from the study participants, and when all the data had been tallied, women who were currently using oral contraception were 15% less likely to have RA than women who were not. In past users of the Pill, the rate was 13% less likely.
Even in women who tested positive for the ACPA (anti-citrullinated protein) antibodies for RA had a lower risk of developing arthritis if they had used the Pill. Research shows that among women who have this antibody, approximately 90% will develop RA, so any reduction in that risk is statistically significant. The decrease in risk was still present even after factors like alcohol use and smoking were considered. Breastfeeding at least one child also provided some risk reduction; however, that benefit was not shown once the same lifestyle factors of smoking and drinking were factored into the dataset.