Oral contraceptive use linked to lower rheumatoid arthritis risk

The use of oral contraceptives may be associated with a reduced risk of rheumatoid arthritis based on findings from a large, population-based, case-control study in Sweden.

The lowered risk for rheumatoid arthritis in the study conducted by Cecilia Orellana, PhD, of the Institute of Environmental Medicine at the Karolinska Institute, Stockholm, and her coauthors applied only to patients who tested positive for anticitrullinated protein antibodies (ACPA) and to those who used oral contraceptives for 7 or more years. The investigators also found a significant reduction in RA risk for women who breastfed their children.

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“All of these findings together support the notion of RA as two different disease entities with different risk factors patterns,” the authors wrote.

The researchers looked at 2,578 women with RA and 4,129 female controls from the Swedish Epidemiological Investigation of RA study and found that women who had ever used OCs had 13% lower odds of developing RA than did women who had never used OCs, even after adjusting for age, residential area, smoking, and alcohol consumption. However, this association was significant only for ACPA-positive RA – where the risk was 16% lower – and not for ACPA-negative disease (Ann Rheum Dis. 2017 Aug 17. doi: 10.1136/annrheumdis-2017-211620).

Duration of oral contraceptive use was also positively associated with a decreased risk of RA; women who had taken OCs for 7 or more years had a 19% lower risk of RA, compared with never users.

However, the authors noted that they only collected information on the use of OCs as a whole and not on particular preparations or doses.

Women who had never used OCs and who had also smoked had more than twofold higher odds of developing RA than did women who had used OCs and who had never smoked. Women who had used OCs but who also smoked were 71% more likely to develop RA.

“Since both smoking and the use of OC have been linked to an increased predisposition to venous thrombotic events (VTE), women with a history of VTEs (especially if they smoke) might be recommended not to use OC by their physician. We can therefore not exclude the possibility that our findings on an interaction between non-OC use and smoking merely reflects that smoking women, who have an increased RA risk, do not receive OC prescription as often. The physiopathology of RA is complex and not fully understood, but our findings may contribute to the knowledge regarding mechanisms of importance for the development of RA,” the authors wrote.

The investigators also saw an influence of breastfeeding on the likelihood of developing RA, with a significant 23% lower odds for the disease among women who breastfed their children for 13 months or more and 7% lower odds in women who had breastfed their children for 7-12 months, compared with those who had breastfed for 0-6 months. Once again, this effect was only significant for ACPA-positive RA.

The study was supported by the Swedish Medical Research Council, the Swedish Research Council for Health, Working Life and Welfare, King Gustav V’s 80-Year Foundation, Vinnova, the Swedish Foundation for Strategic Research, the Swedish Rheumatic Foundation, the Stockholm County Council, the Insurance Company AFA, the Innovative Medicines Initiative, and the National Institutes of Health. The authors said that they had no competing interests.