Body mass index and the risk of rheumatoid arthritis: a systematic review and dose-response meta-analysis

INTRODUCTION: The evidence from published studies on the association between obesity and rheumatoid arthritis has been contradictory. To clarify the association between obesity and rheumatoid arthritis, we conducted a systematic review and dose-response meta-analysis to assess the relationship between body mass index and rheumatoid arthritis risk. METHODS: A systematic literature search of PubMed and Embase (up to 12 July 2014) was performed to identify all eligible published reports. The pooled relative risk results with corresponding 95% confidence intervals of rheumatoid arthritis development were estimated using a random-effects model. RESULTS: Eleven eligible related citations fulfilled the inclusion criteria and were included in the study. Compared with individuals with a body mass index under 30, obese individuals showed an association with a significantly increased risk of rheumatoid arthritis (relative risk = 1.25, 95% confidence interval: 1.07 to 1.45, P(heterogeneity) <0.01, I(2) = 63%). Compared to normal weight subjects, the pooled relative risks for rheumatoid arthritis were 1.31 (1.12 to 1.53) and 1.15 (1.03 to 1.29) for the categories of obese and overweight, respectively. In the dose-response analysis, there was evidence of a nonlinear association (P(nonlinear) = 0.005) and the estimated summary relative risk for a 5-unit increment was 1.03 (95% confidence interval: 1.01 to 1.05, P(heterogeneity) = 0.001, I(2) = 70.0%). CONCLUSIONS: An increase in body mass index can contribute to a higher risk for rheumatoid arthritis development. However, the finding also highlights the need for research on the association between body mass index and rheumatoid arthritis risk with adjustment for more confounding factors. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s13075-015-0601-x) contains supplementary material, which is available to authorized users.