Associations between multiple metals exposure and cognitive function in the middle-aged and older adults from China: a cross-sectional study

The rapidly rising risk of cognitive decline is a serious challenge for the elderly. As the wide-distributed environmental chemicals, the effects of metals exposure on cognitive function have attracted much attention, but the results remain inclusive. This study aimed to investigate the roles of multiple metals co-exposure on cognition. We included a total of 6112 middle-aged and older participants, detected their plasma levels of 23 metals by using inductively coupled plasma mass spectrometry, and assessed their cognitive function by using the Mini-Mental State Examination (MMSE). The results showed that increase plasma levels of iron (Fe) and zinc (Zn) were positively associated with MMSE score, but the increase levels of nickel (Ni) and lead (Pb) were associated with decreased MMSE score (all FDR < 0.05). Subjects exposed to both high levels of Ni and Pb showed the lowest MMSE score [β (95%CI) = -0.310 (-0.519, -0.100)], suggesting that Ni and Pb had a synergistic toxic effect on cognitive function. In addition, the hazardous roles of Ni and Pb were mainly found among subjects with low plasma level of Zn, but were not significant among those with high-Zn level [Ni: β (95% CI) = -0.281 (-0.546, -0.015) vs. -0.146 (-0.351, 0.058); Pb: β (95% CI) = -0.410 (-0.651, -0.169) vs. -0.060 (-0.275, 0.155)], which suggested that Zn could attenuate the adverse effects of Pb and Ni on cognitive function. The cognitive function was gradually decreased among subjects with increased number of adverse exposures to the above four metals (P