Breast‐feeding and the onset of rheumatoid arthritis

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Abstract
Objective. In a recent study we demonstrated that the postpartum period, particularly after the first pregnancy, is a time of increased risk for the development of rheumatoid arthritis (RA). The present study was undertaken to investigate whether this risk might be explained by breast‐feeding. Methods. Through a nationwide media campaign, we identified 187 women who had developed RA within 12 months of a pregnancy, and we compared their breast‐feeding histories with those of 149 similarly aged women chosen from the patient registers of a nationwide group of general practitioners. Results. In all, 88 of the women with RA developed the disease after their first pregnancy. Eighty‐one percent of these 88 women had breast‐fed. This was higher than the breast‐feeding prevalence of 50% in the 129 controls whose first pregnancy had resulted in a live birth (adjusted odds ratio [OR] 5.4, 95% confidence interval 2.5–11.4). There was a smaller increased risk of breast‐feeding after a second pregnancy in the RA cases (OR 2.0) and no increase after a third pregnancy (OR 0.6). The increase in risk was greatest in those cases whose disease was erosive and who were rheumatoid factor positive. Conclusion. In a small group of susceptible women, exposure to breast‐feeding after the first pregnancy is associated with a significant increase in risk for RA development. We postulate that this may reflect hormonal influences, specifically the high level of the proinflammatory hormone prolactin.