Mediation effect of elevated fasting blood glucose on cognitive impairment induced by occupational aluminum exposure among workers

Background Long-term occupational aluminum exposure can not only cause cognitive impairment, but also boost the blood glucose and increase the risk of diabetes in workers. Although the association between diabetes and cognitive impairment has been confirmed, the role of blood glucose increasing in cognitive impairment induced by occupational aluminum exposure has not been identified.

Objective This study aims to identify the role of blood glucose increasing in cognitive impairment induced by occupational aluminum exposure in workers.

Methods A total of 184 male workers were selected from the electrolytic aluminum workshop, alumina workshop, and thermoelectric workshop of a large aluminum plant in Shanxi Province by cluster sampling method in 2019. These workers were asked to complete a questionnaire survey on general information and their blood samples were collected. They were divided into Q₁, Q₂ and Q₃ groups according to plasma aluminum level (< P₂₅, P₂₅-P₇₅, and >P₇₅) determined by inductively coupled plasma mass spectrometry (ICP-MS); fasting blood glucose (FBG) was measured by glucose oxidase method and categorized into three levels (<P₂₅, P₂₅-P₇₅, and >P₇₅). The Montreal Cognitive Assessment Scale (MocA Scale) was used to evaluate the cognitive function of workers; the total possible score of the scale is 30 points, and a score of < 26 indicated cognitive impairment. Multiple logistic regression was used to analyze the relationship between aluminum exposure, FBG, and MocA score, and mediation effect analysis was used to analyze the role of FBG in the correlation between aluminum exposure and MocA score.

Results These workers' medians (P₂₅, P₇₅) of plasma aluminum concentration, FBG concentration, and MocA score were 40.14 (30.71, 49.78) μg·L^-1, 5.02 (4.77, 5.22) mmol·L^-1, and 23 (22, 26), respectively. The multiple logistic regression analysis results showed that plasma aluminum level was positively correlated with FBG level (adjusted OR=1.046, 95% CI: 1.019-1.074), and the risks of cognitive impairment of workers in the Q₂ and the Q₃ groups were 2.096 (2.022-6.045) times and 2.831 (1.091-7.351) times higher than that of the Q₁ group, after adjusting for type of work, age, smoking, drinking, exercise, body mass index, and education. Moreover, the risks of cognitive impairment of workers with high-level (>P₇₅) and intermediate-level (P₂₅-P₇₅) FBG were 2.464 (1.897-8.169) times and 1.889 (1.783-4.558) times higher than that of the low-level FBG group (< P₂₅). The results of mediation effect analysis showed that the mediation effect accounted for 25.1% of the total effect.

Conclusion There are dose-response relationships of aluminum exposure with FBG level and cognitive impairment, and the cognitive impairment induced by aluminum exposure may partially arise from elevated blood glucose.