Objectives: The aim of this study was to determine whether breast-feeding or the use of oral contraceptives (OC) could affect the future risk of rheumatoid arthritis (RA) in a community-based prospective cohort.
Methods: A community based health survey (18 326 women) was linked to regional and national registers, and incident cases of RA were identified. All females with RA diagnosis after inclusion in the health survey (n = 136) and four female controls for every case, who were alive and free from RA when the index person was diagnosed with RA, were included in a case-control study. Data on life style factors at baseline were derived from a self-administered questionnaire. Potential predictors were examined in logistic regression models.
Results: One hundred and thirty-six women with incident RA were compared to 544 age matched controls. Longer history of breast-feeding was associated with a reduced risk of RA (OR: 0.46; 95% CI 0.24-0.91 for women with ≥ 13 months of breast-feeding, and OR 0.74; 95 % CI 0.45-1.20 for those with 1-12 months, compared to those who never breast-fed). The protective effect of longer breast-feeding remained significant when adjusting for smoking and level of education in multivariate models, and point estimates were protective also when restricting the analyses to parous women. Parity or OC use did not have any significant effect on the risk of RA.
Conclusion: In this study, long-term breast-feeding, but not use of OC, was associated with a significant reduction of the risk of RA.