Academic journal article Environmental Health Perspectives

Neurotoxic Metal Coexposures: Claus Henn et Al. Respond

Academic journal article Environmental Health Perspectives

Neurotoxic Metal Coexposures: Claus Henn et Al. Respond

Article excerpt

We thank Dorea for his comments on the importance of examining breast-feeding and ethylmercury exposure in our study of manganese--lead coexposures and neurodevelopment (Claus Henn et al. 2012). We agree that both breast-feeding and organic mercury exposure may affect neurodevelopment and have the potential to act as confounders and/or effect modifiers in analyses of metal effects on neurodevelopment.

To be a confounder, a variable must be associated with both exposure and outcome. In our data, duration of breast-feeding was not strongly associated with exposures (measured by blood manganese and lead levels). When breast-feeding variables were forced into final models, the manganese--lead effect estimates did not change appreciably. Although breast-feeding did not appear to be an important confounder in our data, we agree with Thirea that this factor needs to be considered in studies of prenatal and early life environmental exposures and neurodevelopment.

We agree with Dorea that organic mercury may be an important coexposure, acting potentially as a confounder and/or effect modifier of the manganese--lead association with neurodevelopment. We do not have detailed data on vaccination rates and ages. However, if the primary source of mercury exposure among these participants is via thimerosal-containing vaccines, as Thirea suggests, then in order for mercury to be a confounder, becoming vaccinated must be associated with manganese and lead exposures. …

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