Selenium as a potential protective factor against mercury developmental neurotoxicity.

Experimental studies suggest that selenium (Se) may decrease methylmercury (MeHg) toxicity under certain exposure regimens. In epidemiological studies, the exposure to MeHg occurs from fish and seafood, which are also a source of beneficial nutrients such as selenium. However, little is known about the potential protective effects of dietary Se against MeHg neurotoxicity in humans. The possible interaction was assessed in two birth cohorts in the Faroe Islands, consisting of singleton term births from 1986 to 1987 (N=1,022), and 1994 to 1995 (N=182), respectively. Dietary habits in this fishing population included frequent consumption of seafood, including whale meat high in mercury. Both Hg and Se were measured in cord whole blood. Neurodevelopmental outcomes were evaluated at age 7 years in both cohorts, and the smaller cohort also included neurological assessment on several prior occasions. Each outcome was modeled as a function of Hg and Se interactions (with adjustments for potential risk factors) by expressing the effects of log10(Hg) within the lowest 25%, the middle 50%, and the highest 25% of the Se distribution. Surplus Se was present in cord blood, the average being a 10-fold molar excess above MeHg. Regression analyses failed to show consistent effects of Se, or statistically significant interaction terms between Se and MeHg. Overall, no evidence was found that Se was an important protective factor against MeHg neurotoxicity. Prevention, therefore, needs to address MeHg exposures rather than Se intakes. Because of the benefits associated with fish intake during pregnancy, consumers should be advised to maintain a high fish and seafood intake that is low in Hg contamination. Additional research is needed to determine the identity of the nutrients responsible for the beneficial effects.