Environmental exposure to manganese in adults and cognitive and motor function. A systematic literature review and meta-analysis.

Background/Aim. Whether environmental exposure to Mn in adults is associated with poorer results in cognitive and motor function is unclear. We aimed to determine these associations through a meta-analysis of published studies. Methods: A systematic review was conducted to identify environmental Mnepidemiologic studies in >=18 years old, and in which results on a specific test to evaluate cognitive or motor function were reported. Medline through PubMed, ISI Web of Knowledge and SCOPUS databases were consulted. A manual search in the references of retrieved studies and systematic reviews found that addressed the topic was also conducted. Data were pooled in meta-analysis using the method of random effects or fixed effects, as convenient, after examination of statistical heterogeneity. Results.Seventeen studies fulfill inclusion criteria. Among them, 13 studies reported data susceptible of meta-analysis through a pooled correlation or a Standardized Means Difference (SMD) approach between exposed and non-exposed. Regarding cognitive function, the results of the studies showed heterogeneity among them (I2=76.49%, p<0.001). The overall effect was a statistically significant negative correlation in the random effects model (pooled r=-0.165; 95%CI: -0.214 to -0.116; p<0.001). In terms of SMD, results showed also moderate heterogeneity but did not reach statistical significance under the random effects model (SMD=-0.049; 95%CI: -0.124 to 0.026; p=0.203). Regarding motor function, heterogeneity (I2=75%)was also observed in the correlation approach with a pooled r (random effect model)=-0.150; 95%CI: -0.219 to -0.079. Moderate heterogenety was observed according to SMD approach (I2=51.81%), with a pooled SMD=-0.136; 95%CI: -0.188 to-0.084; p<0.001, indicating worse motor function in exposed. Conclusions: Correlation approach results support a negative effect on cognitive and motor function (the higher the Mn levels, the poorer scores). Regarding SMD approach, results also support a worse cognitive and motor function in exposed, although only for motor function statistical significance was obtained.