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Breast-feeding and the onset of rheumatoid arthritis.

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.