Genetic and environmental factors contribute to the risk of depression and several studies have noted an association between tobacco smoke and depression. Cadmium is a neurotoxicant and the main source of non-occupational exposure is tobacco smoke.

We conducted a cross-sectional analysis of data from 2892 young adult (aged 20–39 years) participants of the National Health and Nutrition Examination Survey (NHANES) 2007–2010. Multivariate logistic regressions, adjusted for age, sex, race/ethnicity, education, poverty income ratio (PIR), obesity, alcohol intake, blood lead (BPb) and smoking status, were used to analyze the association between blood cadmium (BCd) and depressive symptoms, as determined by the score on the nine-item Patient Health Questionnaire (PHQ-9).

Individuals in the highest BCd quartile had higher odds of having depressive symptoms [odds ratio (OR) 2.79, 95% confidence interval (CI) 1.84–4.25] than those in the lowest BCd quartile. Smoking status, but not BPb, was statistically significantly associated with depressive symptoms. Stratification by smoking status found that BCd was significantly associated with depressive symptoms in both non-smokers (OR 2.91, 95% CI 1.12–7.58) and current smokers (OR 2.69, 95% CI 1.13–6.42).

This is the first study to report an association between BCd levels and depressive symptoms using a nationally representative sample. The association of cadmium with depressive symptoms was independent of smoking status. If this association is further confirmed, the continued efforts at reducing cadmium exposures, mainly through tobacco smoking cessation programs, may decrease the incidence of depression.