Associations of mixed metals exposure with risk of cognitive impairment: A cross-sectional study in Chinese adults

Abstract

Abstract Background Associations between exposure to single metals and cognitive impairment or related outcomes have been reported in many previous studies. However, co-exposure to more than one metal is common situation. In recent years, studies on the effects of exposure to multiple metals on cognitive impairment or related outcomes have increased, but remain very limited, with a focus on populations with occupational exposure to metals, children and adolescents. The potential relationships between exposure to metal mixtures and risk of cognitive impairment in adults remain to be clarified. Objectives To investigate the associations of blood metal mixtures with risk of cognitive impairment. Methods A cross-sectional study was conducted in 1104 Chinese adults who underwent routine physical examination in the Kailuan General Hospital in Tangshan. The blood levels of lead (Pb), iron (Fe), copper (Cu), calcium (Ca), magnesium (Mg), zinc (Zn) were measured by the inductively coupled plasma mass spectrometry (ICP-MS). Multivariable logistic regression (MLR) models and Bayesian kernel function regression (BKMR) models were applied to assess the associations. Results A total of 218 participants (19.75%) were diagnosed with cognitive impairment. The median mini-mental state examination (MMSE) rating in cognitive impairment group (25 score) was significantly lower than that in normal cognitive function group (29score). Four metals (Pb, Fe, Cu and Mg) were positively associated with cognitive impairment in single-metal models. Pb and Cu remained significantly positive associations after adjusting for these six metals, with the odds ratios (95% confidence intervals) in the highest quartiles of 9.51 (4.41–20.54, p-trend < 0.01) and 4.87 (2.17–10.95, p-trend < 0.01), respectively. The BKMR models showed that co-exposure levels of Pb, Fe, Cu, Ca, Mg, Zn were associated with increased risk of cognitive impairment when the metal mixtures were ≥ 25th percentile compared to their medians, and Pb and Cu were the major contributors to the joint effect. In addition, interaction effects of Mg and Pb, Pb and Cu on the risk of cognitive impairment were observed. Conclusions Co-exposure of six metals (Pb, Fe, Cu, Ca, Mg and Zn) increased the risk of cognitive impairment in Chinese adults, with Pb and Cu likely to have greater impact. Potential interaction effects of Mg and Pb, Pb and Cu on the risk of cognitive impairment may exist.