Dietary selenium's protective effects against methylmercury toxicity
Ralston NVC, Raymond LJ (2010) Toxicology 278(1) 112-23. doi: 10.1016/j.tox.2010.06.004. Epub 2010 Jun 16.
Abstract:
Dietary selenium (Se) status is inversely related to vulnerability to methylmercury (MeHg) toxicity. Mercury exposures that are uniformly neurotoxic and lethal among animals fed low dietary Se are far less serious among those with normal Se intakes and are without observable consequences in those fed Se-enriched diets.Although these effects have been known since 1967, they have only lately become well understood. Recent studies have shown that Se-enriched diets not only prevent MeHg toxicity, but can also rapidly reverse some of its most severe symptoms.
It is now understood that MeHg is a highly specific, irreversible inhibitor of Se-dependent enzymes (selenoenzymes). Selenoenzymes are required to prevent and reverse oxidative damage throughout the body, particularly in the brain and neuroendocrine tissues. Inhibition of selenoenzyme activities in these vulnerable tissues appears to be the proximal cause of the pathological effects known to accompany MeHg toxicity.
Because Hg's binding affinities for Se are up to a million times higher than for sulfur, its second-best binding partner, MeHg inexorably sequesters Se, directly impairing selenoenzyme activities and their synthesis.
This may explain why studies of maternal populations exposed to foods that contain Hg in molar excess of Se, such as shark or pilot whale meats, have found adverse child outcomes, but studies of populations exposed to MeHg by eating Se-rich ocean fish observe improved child IQs instead of harm.
However, since the Se contents of freshwater fish are dependent on local soil Se status, fish with high MeHg from regions with poor Se availability may be cause for concern. Further studies of these relationships are needed to assist regulatory agencies in protecting and improving child health.
FAB RESEARCH COMMENT:
Ocean fish and other seafood are rich dietary sources of selenium - and as this article explains
- selenium protects against the potentially neurotoxic effects of methymercury, a possible contaminant that some types of fish and seafood may contain.
This helps to explain why no harmful effects on children's brain development have been observed from fish ans seafood consumption during pregnancy - even at very high intakes (as found in the Seychelles, for example - or in women eating traditional Japanese diets)
In the US and UK, official dietary advice on fish and seafood consumption in pregnancy still includes cautions about avoiding some types of fish, emphasising the possible risks from methylmercury or other environmental contaminants.
However, all the available data on both maternal and child outcomes show that the nutritional benefits of fish and seafood outweigh the theoretical risks.
Data from a large UK birth cohort study found that the more fish and seafood mothers ate during pregnancy, the better were the neurodevelopmental outcomes for their children, across a wide range of measures. See:
And for more information on fish and seafood in pregnancy, please see the following article lists, which are frequently updated.
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