A path analysis of multiple neurotoxic chemicals and cognitive functioning in older US adults (NHANES 1999–2002)

BACKGROUND Polychlorinated biphenyls (PCBs) and metals (lead and cadmium) are neurotoxic and affect neurobehavioral performance. Yet little is known about the association between exposure to multiple neurotoxic compounds and cognitive functioning in older adults. METHODS Using data from two consecutive cycles of the National Health and Nutrition and Examination Survey (1999-2002), path analysis was used to simultaneously evaluate the association between whole blood concentrations of 14 neurotoxic compounds and cognitive functioning measured by the Digit Symbol Coding Test of the Weschler Adult Intelligence Scale, 3rd Edition in participants 60-84 years of age (N = 498). Effect modification was assessed for age (above/below the mean) and sex. RESULTS The final path model fit 5 compounds (i.e. PCB 74, PCB 118, PCB 146, PCB 153, and lead). After controlling for co-exposures and confounders, PCB 146 (β = -0.16, 95% CI: -0.29, -0.02, p = 0.02) and lead (β = -0.10, 95% CI: -0.20, -0.006, p = 0.04) were negatively associated with DSC scores in 60-84 year olds. Whereas, PCB 153 was positively associated with DSC scores (β =0.20, 95% CI: 0.05, 0.35; p = 0.01). CONCLUSIONS This cross-sectional analysis which controlled for collinear exposure to several neurotoxic compounds demonstrated an association between non-dioxin like polychlorinated biphenyl exposure, specifically PCB 146, and lower cognitive functioning, in older adults. Lead exposure was also weakly associated with lower cognitive functioning. Additional studies are needed to determine the causality of the observed associations.