Abstract
Background/Objective: Whether environmental exposure to Manganese (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 epidemiological studies on a population ≥18 years old exposed to environmental airborne Mn, and in which results on specific tests to evaluate cognitive or motor functions were reported. We consulted Medline through PubMed, Web of Science and SCOPUS databases. We also performed a manual search within the list of bibliographic references of the retrieved studies and systematic reviews. To weight Mn effects, a random effects versus fixed effect model was chosen after studying the heterogeneity of each outcome. Results. Eighteen studies met the inclusion criteria. Among them, eleven studies reported data susceptible for meta-analysis through a pooled correlation or a standardized means difference (SMD) approach between exposed and non-exposed groups. 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). For SMD, the results showed a lower heterogeneity with a negative SMD that did not reach statistical significance under the fixed effects model (SMD = −0.052; 95%CI −0.108 to 0.004; p = 0.068). 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; p < 0.001. Moderate heterogeneity was observed according to the SMD approach (I2 = 52.28%), with a pooled SMD = −0.136; 95%CI: −0.188 to−0.084; p < 0.001, indicating worse motor function in those exposed. Conclusions: Correlation approach results support a negative effect on cognitive and motor functions (the higher the Mn levels, the poorer the scores). Regarding the SMD approach, results also support a worse cognitive and motor functions in those exposed, although only for motor function statistical significance was obtained.
Highlights
IntroductionManganese (Mn) is a trace element, and essential for our normal physiological function [1], being implicated in physiological processes, related to reproduction and development (e.g., formation of healthy cartilage and bone), energy metabolism (e.g., pyruvate carboxylase), urea cycle (e.g., arginase), and antioxidative capacity (e.g., Mn superoxide dismutase) [2]
Manganese (Mn) is a trace element, and essential for our normal physiological function [1], being implicated in physiological processes, related to reproduction and development, energy metabolism, urea cycle, and antioxidative capacity (e.g., Mn superoxide dismutase) [2]
Most of the studies from the same countries were based on the same geographical areas or exposed population
Summary
Manganese (Mn) is a trace element, and essential for our normal physiological function [1], being implicated in physiological processes, related to reproduction and development (e.g., formation of healthy cartilage and bone), energy metabolism (e.g., pyruvate carboxylase), urea cycle (e.g., arginase), and antioxidative capacity (e.g., Mn superoxide dismutase) [2]. With regard to environmental exposure to high levels of Mn, an increasing number of epidemiological studies have been published in recent decades, both in children and in adult populations, focusing mainly on neurological effects on cognitive and motor functions [10]. In the meta-analysis, which included 55 primary studies published until 31 December 2019, the results from their included cohort studies support an association between higher Mn levels and a negative effect on neurodevelopment, especially regarding cognitive and motor skills for children under six years old, as indicated by several metrics, the need for prospective studies, ideally with repeated measures of exposures, confounders, and outcomes over time, was highlighted [12]. To our knowledge, there is no published meta-analysis
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