Incidence and prevalence rates of pSS vary widely around the world. The results help us better understand the global epidemiology of pSS. Large population-based studies combining meticulous case-finding and case-ascertainment strategies are needed.

IntroductionThe 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.MethodsA 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.ResultsEleven 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, Pheterogeneity <0.01, I2 = 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 (Pnonlinear = 0.005) and the estimated summary relative risk for a 5-unit increment was 1.03 (95% confidence interval: 1.01 to 1.05, Pheterogeneity = 0.001, I2 = 70.0%).ConclusionsAn 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 materialThe online version of this article (doi:10.1186/s13075-015-0601-x) contains supplementary material, which is available to authorized users.

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The present metaanalysis indicates that PM and DM are significantly associated with increased risks of overall malignancy and most site-specific malignancies. The number of studies on association between PM or DM and some malignancies is too small to draw a firm conclusion. Accordingly, more research is needed for these malignancies.

This meta-analysis indicates that pSS is significantly associated with increased risks of overall malignancy, NHL and thyroid cancer. However, it is not yet known whether the apparent increased risk of overall malignancy in patients with pSS is due to the relatively high prevalence of NHL in that group.