Single and joint exposure of Pb, Cd, Hg, Se, Cu, and Zn were associated with cognitive function of older adults

Impaired cognitive function following exposure to heavy metals has emerged as a significant global health concern. Nevertheless, the impact of combined exposure to multiple heavy metals on cognitive impairment remains unclear.

This study aimed to explore the association between multiple heavy metals exposure and cognitive function to provide theoretical evidence to guide prevention strategies.

The blood levels of lead (Pb), cadmium (Cd), mercury (Hg), selenium (Se), copper (Cu) and zinc (Zn) and the results of the cognitive function tests were extracted from 811 elderly Americans who completed the NHANES between 2011 and 2014. Quantile regression (QR), restricted cubic splines (RCS), and Bayesian kernel machine regression (BKMR) were used to explore the individual and joint association between heavy metals exposure and performance in 4 standardized cognitive tests; Item Response Theory (IRT), Delayed Recall Test (DRT), Animal Fluency Test (AFT) and Digit Symbol Substitution Test (DSST).

A negative association was noted between Cd levels and IRT (p = 0.048, 95%CI: -2.7, -0.1). Se concentrations ranging between 2.197 µg/L (95%CI: 0.004, 0.15) to 2.29 µg/L (95%CI: 2.56, 7.64) (log₁₀Se) was postively associated with DSST (p = 0.001 ). Cu was negatively associated with DSST (p = 0.049, 95%CI: -37.75, -0.09), while Zn was positively associated with IRT (p = 0.022, 95%CI: 0.55, 11.73). Exposure to the 6 heavy metals combined showed a positive linear association with IRT, DRT, and a negative linear association with DSST. An interaction between Cd and the other heavy metals (excepted for Pb).

Exposure to Pb, Cd, Hg, Se, Cu, and Zn was associated with cognitive function. Joint exposure to the 6 heavy metals showed a positive linear association with IRT, DRT, contrarily, a negative linear association with DSST.