Association between aluminium exposure and cognitive functions: A systematic review and meta-analysis

Chronic Aluminium (Al) exposure is reported to be linked with neuro-cognitive impairment. However, there is limited synthesized information on the role of chronic Al exposure on individual cognitive domains. This knowledge gap is explored here by systematic review and meta-analysis of the published literature. Observational studies that reported the association between Al exposure and cognitive functions were systematically searched in PubMed, Scopus and Embase databases since inception to June 2019 and updated on September 2020. PRISMA guidelines were adhered in this study. Meta-analysis was performed using a random-effect model if the included studies exhibited heterogeneity, in the absence of heterogeneity fixed effect model was used. Heterogeneity was assessed using Cochran-Q test and I2 statistic. Risk of bias was assessed using the risk of bias in non-randomized studies of exposures. Sub-group analysis and meta regression analysis were explored. Twenty-three studies including 1781 Al exposed and 1186 unexposed were part of the final results. The pooled standardized mean difference of global cognitive scores (−0.65, 95%CI: −1.09 to −0.22, I2 = 91.09%), memory (−0.45, 95% CI: −0.69 to −0.21, I2 = 81.67%), working memory (−0.3, 95%CI: −0.45 to −0.15, I2 = 0%) and processing speed domains were significantly inferior among Al exposed as compared to unexposed. The other evaluated cognitive domains, such as cognitive flexibility, visuospatial abilities and psychomotor functions did not significantly differ between the two groups. We observed a serious risk of bias in most of the included studies. Current pieces of evidence suggest an association between chronic Al exposure and impaired cognitive function in majority of domains including memory, processing speed and working memory while no significant influence in other cognitive domains. However, considering high heterogeneity and low quality of primary evidence, further high-quality studies are necessary for conclusive evidence in this regard.