Selenium Health Benefit Values: Updated Criteria for Mercury Risk Assessments

Abstract

Selenium (Se)-dependent enzymes (selenoenzymes) protect brain tissues against oxidative damage and perform other vital functions, but their synthesis requires a steady supply of Se. High methylmercury (CH ₃Hg) exposures can severely diminish Se transport across the placenta and irreversibly inhibit fetal brain selenoenzymes. However, supplemental dietary Se preserves their activities and thus prevents pathological consequences. The modified Se health benefit value (HBV _Se) is a risk assessment criterion based on the molar concentrations of CH ₃Hg and Se present in a fish or seafood. It was developed to reflect the contrasting effects of maternal CH ₃Hg and Se intakes on fetal brain selenoenzyme activities. However, the original equation was prone to divide-by-zero-type errors whereby the calculated values increased exponentially in samples with low CH ₃Hg contents. The equation was refined to provide an improved index to better reflect the risks of CH ₃Hg exposures and the benefits provided by dietary Se. The HBV _Se provides a biochemically based perspective that confirms and supports the FDA/EPA advice for pregnant and breast-feeding women regarding seafoods that should be avoided vs. those that are beneficial to consume. Since Se can be highly variable between watersheds, further evaluation of freshwater fish is needed to identify locations where fish with negative HBV _Se may arise and be consumed by vulnerable subpopulation groups.