Dose-response meta-analysis between body mass index and rheumatoid arthritis risk. (a) RR of RA risk per 5 kg/m2 increase in BMI; (b) nonlinear dose-response association, BMI was modeled with a nonlinear trend (black continuous line) in a random-effects meta-regression model. Long-dashed black lines represent 95% confidence intervals. Short-dashed black lines represent the linear trend. The vertical axes are on a log scale. BMI: body mass index; RA: rheumatoid arthritis; RR: relative risk. ES: Effect Size.