Background The association of long-term effects of inorganic arsenic (iAs) exposure with type 2 diabetes mellitus (T2DM) risk remains controversial.

Methods A literature search was performed in PubMed, China National Knowledge Infrastructure and Web of Knowledge for relevant available articles published in English or Chinese from 1 January 1990 to 5 June 2013. Case-control, cohort or cross-sectional studies evaluating iAs and T2DM were included. The DerSimonian and Laird random effect model was adopted as the pooling method. Dose-response relationship was assessed by restricted cubic spline model and multivariate random-effect meta-regression.

Results Of the 569 articles identified through searching databases, 17 published articles with 2 243 745 participants for iAs in drinking water and 21 083 participants for total arsenic (tAs) in urine were included for this meta-analysis. The pooled relative risk with 95% CI of T2DM for the highest versus lowest category of iAs exposure level in drinking water was 1.75 (1.20 to 2.54). After removing three studies that had a strong effect on heterogeneity, the pooled relative risk was 1.23 (1.12 to 1.36). Dose–response analysis suggested T2DM risk increased by 13% (1.13 (1.00 to 1.27)) for every 100 µg/L increment of iAs in drinking water. Significant association of T2DM risk with tAs in urine was also found 1.28 (1.14 to 1.44).

Conclusions This meta-analysis indicates that long-term iAs exposure might be positively associated with T2DM risk.