Verbal Memory and Learning in Schoolchildren Exposed to Manganese in Mexico
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Manganese (Mn) is an essential nutrient for cellular function, but in high concentrations, it is neurotoxic. Environmental exposure to Mn has been associated with cognitive effects in children. This study aimed to assess the effect of environmental exposure to Mn on verbal memory and learning in schoolchildren residents from two municipalities in the state of Hidalgo, Mexico. Cross-sectional studies were conducted in 2006 and 2013 with a total of 265 schoolchildren of 7 to 11 years old. Children’s Auditory Verbal Learning Test-2 (CAVLT-2) was used to assess verbal memory and learning. Mn exposure tertiles were defined according to hair manganese (MnH) levels determined by atomic absorption spectrophotometry. Linear regression models were used to estimate the association between MnH levels and CAVLT-2 scores. The models were adjusted by potential confounders. The lowest and highest exposure tertiles were defined below and above MnH levels of ≤ 0.72 and ≥ 3.96 μg/g, respectively. Mn exposure was significantly associated with an average of 5- to 9-point decrease in learning curves and summary CAVLT-2 scores in the highest tertile. This study adds to the evidence of decreased verbal memory and learning in schoolchildren environmentally exposed to manganese.
KeywordsHair manganese Mining area Verbal memory Verbal learning Schoolchildren
Central Nervous System
Children’s Auditory Verbal Learning Test-2
Micrograms per gram
Micrograms per deciliter
Grams per deciliter
Our special thanks to all families who participated in this study, and the teachers of the elementary schools “Gral. Ignacio Manuel Altamirano” and “Belisario Dominguez” for all the assistance offered. We thank SJ. Velázquez-Juárez for the design of the study area map. We thank the support of the children’s environmental health Mexico thematic network to publish this paper (CONACyT-Mexico project number 271626).
This project received funding from the International Development Research Centre (IDRC) project number 100662 and the Consejo Nacional de Ciencia y Tecnología (CONACYT) project number 141385. The funding agencies have not participated in the methodological design of this research.
Compliance with Ethical Standards
Conflict of Interest
The authors declare that they have no conflict of interest.
All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.
Bioethics and Research Committees
This study was approved by the Bioethics and Research Committees of the National Institute of Public Health from Mexico.
Informed consent was obtained from all individual participants included in the study.
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