Background Breastfeeding has been associated with both a decreased [1,2] and an increased  risk of developing RA. To our knowledge no previous study has investigated the impact of breastfeeding on the two subgroups of RA, characterized by presence/absence of antibodies to citrullinated peptides (ACPA).
Objectives To study the association between breastfeeding and the risk of ACPA-positive and ACPA-negative RA among women aged 18-70.
Methods Data from the population-based EIRA (Epidemiological Investigation of RA) case-control study was analyzed. In total, 938 incident cases and 1917 controls participated between 2006-2011. An extensive questionnaire was answered by the participants, including questions regarding duration of breastfeeding for each delivered child and potential confounders (education, smoking, BMI, oral contraceptive use, postmenopausal hormone therapy, reproductive factors). Total history of breastfeeding was categorized into 0-3, 4-7, 8-12, 13-19 and ≥20 months, using the lowest category as the reference group. We calculated odds ratios (ORs) with 95% confidence intervals (CI) by means of unconditional logistic regression, adjusting for age, residential area and number of children.
Results A longer duration of breastfeeding was associated with a decreased risk of ACPA-positive RA (OR 4-7 months=1.0, 95% CI 0.7-1.4; OR 8-12 months=0.8, 95% CI 0.6-1.2; OR 13-19 months=0.6, 95% CI 0.4-0.9; OR ≥20 months=0.7, 95% CI 0.4-1.0) compared to parous women who breastfed less than 3 months. No association between breastfeeding and ACPA-negative RA was found.
Conclusions Our results indicate that a longer duration of breastfeeding reduces the risk of ACPA-positive RA among parous women, but has no association with the risk of ACPA-negative RA. Further research is needed to explore the biological mechanisms behind our findings but our study contributes to the knowledge of environmental risk factors such as breastfeeding and its different impact on the subgroups of RA.
Pikwer M, et al. Breast feeding, but not use of oral contraceptives, is associated with a reduced risk of rheumatoid arthritis. Ann Rheum Dis. 2009;68(4):526-30.
Karlson EW, et al. Do breast-feeding and other reproductive factors influence future risk of rheumatoid arthritis? Results from the Nurses' Health Study. Arthritis Rheum. 2004;50(11):3458-67.
Berglin E, et al. Influence of female hormonal factors, in relation to autoantibodies and genetic markers, on the development of rheumatoid arthritis in northern Sweden: a case-control study. Scand J Rheumatol. 2010 Nov;39(6):454-60.
Acknowledgements We want to thank Marie-Louise Serra and Lena Nise for excellent assistance in collection of data. We also thank all the cases and controls who participated in the study as well as clinicians and nurses part of the Epidemiological Investigation of Rheumatoid Arthritis study group.
Disclosure of Interest None declared