Association of single and combined effects of blood heavy metals with cognitive function in older adults of the United States: A cross-sectional study

Abstract Background Heavy metal exposure has been associated with various diseases. The purpose of this study was to determine the single and combined effects between blood heavy metals and cognitive function in older adults. Methods This observational study utilizes data from the National Health and Nutrition Examination Survey (NHANES) between 2011 and 2014 and involved 1460 participants aged ≥ 60 years. The concentrations of blood lead (Pb), cadmium (Cd), mercury (Hg), selenium (Se), and manganese (Mn) were measured using inductively coupled plasma mass spectrometry (ICP-MS). Cognitive function was assessed using the immediate Recall test (IRT), delayed recall test (DRT), animal fluency test (AFT), and digit symbol substitution test (DSST). Linear regression, restricted cubic spline (RCS), and subgroup analyses were used to assess the relationship between blood heavy metal concentrations and cognitive function. Results Multiple linear regression analysis showed a negative correlation between Cd concentrations and comprehensive cognitive scores (β=-2.698, 95% CI: -4.842, -0.554). Blood Se levels were positively correlated with comprehensive cognitive scores (β = 0.049, 95% CI: 0.022, 0.076) and all four cognitive domains. The RCS showed that the dose-response association between Cd and comprehensive cognitive scores appeared to be linear (P-nonlinear = 0.566), while Se exhibited a parabolic shape tilted to the left relationship with comprehensive cognitive scores (P-nonlinear = 0.013). Conclusions A high concentration of Cd is strongly associated with cognitive decline. However, the protective effect of Se on cognitive function plateaus after reaching a certain concentration. These findings may have significance for the development of interventions aimed at alleviating cognitive impairment.