Cadmium exposure, fasting blood glucose changes, and type 2 diabetes mellitus: A longitudinal prospective study in China

Background: Cadmium is a recognized human carcinogen, raising global concern for its ubiquitously environmental exposure on public health. Diabetogenic effects of cadmium have been suggested in previous studies, but the longitudinal associations of chronic cadmium exposure with fasting blood glucose changes and type 2 diabetes mellitus have not been fully elucidated. Objective: To investigate the effects of long-term cadmium exposure on the fasting blood glucose changes and type 2 diabetes mellitus risk in a longitudinal prospective study of China. Methods: A total of 3521 urban adults were included as baseline study population from the Wuhan-Zhuhai cohort, and followed up three years later. Urinary cadmium concentrations were determined repeatedly during the follow-up of a three-year period. The within-person and between-person variability of urinary cadmium concentrations over three years was estimated using multilevel random-effects mixed models. Multivariate regression models were performed to evaluate the associations of cadmium exposure with fasting blood glucose changes and type 2 diabetes mellitus risk. Results: The geometric means of creatinine-corrected urinary cadmium concentration at baseline were 1.13 mu g/g creatinine, which were close to the levels of follow-up (1.14 mu g/g creatinine). The intra-class correlation coefficient of creatinine-corrected urinary cadmium concentrations was 0.71, achieving good reproducibility of cadmium over three years. With adjustment for potential confounders, each one-unit increase in log10-transformed cadmium was associated with a 0.11 (95%CI: 0.03 to 0.19) elevation in fasting blood glucose concentration, and was associated with a 42% (95%CI: 1.16 to 1.73) increase in risk of prevalent type 2 diabetes mellitus. Upward trends of fasting blood glucose changes and type 2 diabetes mellitus incidence were observed with increasing cadmium exposure. Individuals with the highest urinary cadmium exposure had a significant increase in fasting blood glucose change at follow-up [beta (95% CI): 0.49 (0.31-0.67)]. Risk of incident type 2 diabetes mellitus were gradually elevated across increasing quartiles of cadmium exposure, though associations did not reach statistical significance (P = 0.15). Conclusions: Our findings suggested that relatively high chronic cadmium exposure for general population adults might contribute to elevated changes of fasting blood glucose resulting in the development of type 2 diabetes mellitus.