Association between cadmium exposure and urolithiasis risk: A systematic review and meta-analysis

Background: We performed a meta-analysis to determine whether a consistent relationship exists between cadmium exposure and urolithiasis in humans. Accordingly, we summarized and reviewed previously published quantitative studies. Methods: Eligible studies with reference lists published before June 1, 2017 were obtained from searching several databases. Random effects models were used to summary the overall estimate of the multivariate adjusted odds ratios (ORs) with 95% confidence intervals (CIs). Results: Six observational studies involving 88,045 participants were identified and stratified into the following categories according to cadmium assessment results: occupational (n=4) and dietary (n=2). The findings of the meta-analysis suggested that the risk of urolithiasis increases significantly by 1.32 times at higher cadmium exposure (OR=1.32; 95% CI=1.08-1.62; for highest vs lowest category urinary cadmium values). The summary OR in occupational exposure (OR=1.56; 95% CI=1.13-2.14) increased at the same condition. Meanwhile, no association was observed between cadmium exposure and urolithiasis risk in dietary exposure (OR=1.13; 95% CI=0.87-1.47). A significant association remained consistent, as indicated by subgroup analyses and sensitivity analyses. Conclusions: The meta-analysis indicated that increased risk of urolithiasis is associated with high cadmium exposure, and this association is higher in occupational exposure than in dietary exposure. Nevertheless, well-designed observational studies with different ethnic populations are still needed.