The Relationship between Plasma Al Levels and Multi-domain Cognitive Performance among In-service Aluminum-exposed Workers at the SH Aluminum Factory in China: A Cross-sectional Study

Background: Aluminum (Al) exerts neurotoxic effects following overexposure. We previously reported worse cognitive performance in workers exposed to Al than non-exposed individuals. Cognition involves multiple domains. The effect of Al on multi-domain cognition has been studied for decades, but still remains controversial. Objective: To explore the relationship between plasma Al levels and multi-domain cognitive performance among in-service aluminum-exposed workers at the SH Aluminum Factory in China and identify possible types of early cognitive damage caused by exposure to aluminum. Methods: Eight hundred thirty-one in-service aluminum-exposed workers at the SH Aluminum Factory in China were investigated. The plasma Al concentrations were measured using inductively coupled plasma-mass spectrometry (ICP-MS) and served as an internal exposure indicator. The participants were divided into four subgroups based on the quartiles of plasma Al concentrations, namely, the Q(1), Q(2), Q(3), and Q(4) subgroups. Cognitive function was assessed using the Mini-mental State Examination (MMSE) and the clock-drawing test (CDT). Multi-domain cognition was evaluated using sub-tests of the MMSE and the CDT. Results: The average plasma Al concentration was 15.26 (8.28, 27.02) mu g/L. The neurobehavioral tests showed negative correlations between plasma Al levels and total CDT scores and executive/visuospatial cognitive performance, and a positive correlation between plasma Al levels and CDT-position errors (all P < 0.05). Additionally, dose-response relationships between higher plasma Al levels and lower total CDT scores, worse executive/visuospatial cognitive performance, and more error rates in the CDT-position were observed (all P-trend < 0.05). However, no significant correlations or trends were observed between plasma Al levels and other cognitive domains (all P > 0.05). The results from the multivariate logistic regression model and restricted cubic spline models of dose-response relationships were consistent with the results obtained from the general linear model. All potential confounders, such as age, marital status, education, income, type of work, and smoking and drinking habits, were considered. Conclusion: Based on the results, aluminum exposure may exert a substantial effect on impairing executive/visuospatial functions in multi-domain cognition at the early stage, particularly the identification of spatial positions.