Nutrition as a Modifying Factor in Epidemiologic Studies of Chemical Exposures and Nervous System Health Outcomes: an Evidence Map
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Vulnerable populations can experience greater exposure to exogenous chemicals or increased susceptibility to developing adverse health effects from chemical exposures. For these populations, nutrition may play a role in modifying the association between chemicals and neurological health outcomes, with the potential to increase or decrease disease risk. An evidence map was developed to identify such nutritional factors, for potential use in future chemical risk assessments.
A literature search strategy was developed, incorporating terms related to nutrition, chemical exposures, and the nervous system. More than 32,000 studies were identified via PubMed and Web of Science. Population, exposure, comparator, and outcome (PECO) screening criteria were applied to identify epidemiological studies examining joint associations between any ingested environmental chemical, any dietary factor (e.g., vitamins, fatty acids), and any nervous system effect(s). During the title/abstract review, 1,800 of the initial studies were found to meet PECO criteria, and 71 epidemiological studies were included during the full-text review. Study characteristics, including chemical names, specific nervous system outcomes, and dietary factors, were extracted from the included studies.
Evidence mapping revealed that the most frequently studied chemicals in the human studies were methylmercury, lead, and arsenic. Additionally, polyunsaturated fatty acids (PUFAs), selenium, and fish were the most studied dietary modifiers. Based on the findings of this evidence map, future steps include a quantitative analysis to evaluate potential joint effects of chemical exposures and nutrition on the nervous system.