Association between environmental cadmium exposure and increased mortality in the U.S. National Health and Nutrition Examination Survey (1999-2018).

Background: Cadmium (Cd) is toxic to human health and increases overall mortality. In this study, we investigated the association between Cd exposure and all-cause, cardiovascular (CVD), and cancer mortality in the general population and the mediating effect of smoking on these association.

Methods: We used data from U.S. National Health and Nutrition Examination Survey for 1999-2018. To evaluate the hazard ratio (HR) for mortality, a multiple Cox regression analysis was conducted by adjusting for age, sex, race/ethnicity, body mass index, smoking, alcohol, hypertension, diabetes, hyperlipidemia, and history of CVD and cancer. A causal mediation analysis was performed to estimate the effects of smoking.

Results: Among the 31,637 subjects, 5452 (12.3%) died. Blood Cd concentrations were significantly associated with all-cause (HR 1.473, 95% confidence interval [CI] 1.403-1.546, p < 0.001), CVD (HR 1.445, 95% CI 1.344-1.554, p < 0.001), and cancer (HR 1.496, 95% CI 1.406-1.592, p < 0.001) mortality. Urinary Cd concentrations were also significantly associated with them. Using feature selection via machine learning, the importance of Cd in all-cause and cancer mortality was second only to age. The association between Cd concentrations and all-cause mortality was significant in both ever-smokers and never-smokers. The mediating effect of smoking was estimated at 32%, whereas a large proportion (68%) remained a direct effect of Cd. In a subgroup analysis of subjects with cancer history, blood Cd concentrations were significantly associated with cancer-related deaths in those with a history of breast, gastrointestinal, and skin cancers.

Conclusion: High Cd exposure is an important risk factor for all-cause, CVD, and cancer mortality among the general population. Cd exposure increased the risk of death even in never-smokers, and its effects unrelated to smoking were substantial, suggesting the importance of regulating other sources of Cd exposure such as food and water.

Impact Statement: Using national large-scale data, we found that low-level environmental exposure to cadmium significantly increased the risk of all-cause, cardiovascular, and cancer mortality in the general population even after adjusting for several risk factors. Although smoking is a major source of cadmium exposure, cadmium was nevertheless significantly associated with all-cause mortality in never-smokers, and the mediating effect of smoking on this association was only 32%. Hence, other sources of cadmium exposure such as food and water may be important.