Introduction: The association between cadmium levels in the body and diabetes has been extensively studied, with sometimes contrasting results. Smoking is the primary non-occupational source of cadmium, and constitutes a risk factor for diabetes. One can therefore hypothesize that the putative association with cadmium is actually explained by tobacco. To fully control for this confounding factor, we studied the relationship between blood cadmium and glycated haemoglobin (HbA1c) levels separately in never-, former and current smokers.
Methods: We studied a sample of 2749 middle-aged adults from the cross-sectional ELISABET survey in and around the cities of Lille and Dunkirk; none had chronic kidney disease or a history of haematological disorders, and none were taking antidiabetic medication. The blood cadmium level-HbA1c associations in never-, former and current smokers were studied in separate multivariate models. The covariables included age, sex, city, educational level, tobacco consumption (or passive smoking, for the never-smokers), body mass index, estimated glomerular filtration rate, and (to take account of the within-batch effect) the cadmium batch number.
Results: In the multivariate analysis, a significant association between cadmium and HbA1c levels was found in all three smoking status subgroups. A 0.1 μg/L increment in blood cadmium was associated with an HbA1c increase [95% confidence interval] of 0.016% [0.003; 0.029] among never-smokers, 0.024% [0.010; 0.037] among former smokers, and 0.020% [0.012; 0.029] among current smokers.
Conclusions: The observation of a significant association between the blood cadmium concentration and HbA1c levels in a group of never-smokers strengthens the hypothesis whereby diabetes is associated with cadmium per se and not solely with tobacco use. The small effect size observed in our population of never smokers with low levels of exposure to cadmium suggested that the risk attributable to this metal is not high. However, the impact of exposure to high cadmium levels (such as occupational exposure) on the risk of diabetes might be of concern.
Keywords: Cadmium; Confounding factor; Diabetes; Epidemiology; Tobacco.
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