Previous studies into the relationship between hormonal factors and risk of rheumatoid arthritis (RA) have provided conflicting results.
In a study published in the Annals of the Rheumatic Diseases (online, 17 August 2017), researchers explored the effects of oral contraceptives in 2,641 women with incident RA and 4,251 matched controls; and effects of breastfeeding in 884 women and 1,949 controls
Women who had used oral contraceptives had a decreased risk of a subtype of RA called ACPA-positive, but not of ACPA-negative RA, compared with those who had never used them. Long-term use of oral contraceptives was associated with a significantly decreased risk of both types of RA. However, breastfeeding was not associated with RA after adjustment for confounding factors.
The team said these findings supported the idea that RA was two different disease entities with separate risk factors, which could explain the disparity in the findings of previous research.
 Orellana C, Saevarsdottir S, Klareskog L et al. Oral contraceptives, breastfeeding and the risk of developing rheumatoid arthritis: results from the Swedish EIRA study. Ann Rheum Dis 2017. doi:10.1136/annrheumdis-2017-211620