Selenium and mercury and eating fish

Ocean fish – salmon, herring, mackerel, and sardines – are good sources of the omega-3 fatty acids EPA and DHA that have been associated with healthy fetal development, healthy cardiovascular function, and healthy ageing.  Whatever mercury there is in these fish has bound with the selenium in the fish.   This chemical binding has rendered the mercury harmless but has also depleted the amount of selenium available for absorption.

Too many of us are missing out on the health benefits of the omega-3 fatty acids available to us from eating certain types of fish a couple of times a week.  Why are we avoiding fish?  Because many of us are afraid of “eating mercury” in the fish.

It turns out, there is research to show that this is a misconception.  Professor Nick Ralston and his colleagues at the University of North Dakota’s Energy and Environmental Research Center have measured and evaluated the molar ratios of selenium in fish to the mercury in fish [Ralston 2007, 2016].

Their studies show that many of the edible ocean fish have an abundance of selenium in relation to mercury.  So, not only are we missing out on the omega-3 fatty acid benefits, we are also missing out on a good source of dietary selenium [Berry 2008].

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Selenium and heavy metals and childbirth

Studies show that higher concentrations of dangerous heavy metals — cadmium, mercury, and lead — in the blood of the mother are likely to be duplicated in the umbilical cord blood, in the blood of the fetus, in the breast milk, and in the blood of the newborn child, with potentially harmful long-term consequences for the child. There is evidence that selenium binds with cadmium and mercury and enables their elimination from the mothers’ bodies.

Early exposure to natural elements that are toxic – cadmium, mercury, and lead – can have long-term adverse health consequences.  Children exposed to these elements while still in the uterus and while breast-feeding may suffer lasting damage to the brain and nervous system and to the kidneys and liver.  The question is: to what extent can selenium supplementation reduce the risk of toxic damage?

Given the dangerous nature of these poisonous heavy metals – cadmium, mercury, and lead – both for the mother and for the fetus and the neonate, it is difficult to carry out randomized controlled studies.  Instead, the best evidence we have for the beneficial effects of selenium supplementation comes from studies that relate the degree of exposure and the selenium status of the mother and the child.

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Selenium: protection against the accumulation of mercury in the body

Even relatively low exposure to mercury during pregnancy can impair the development of the baby’s brain and nervous system. Fortunately, supplementation with a high-selenium yeast preparation has been shown to reduce significantly the accumulation of mercury in the tissues in the body.

Mercury.  In the form of methylmercury, it is a very harmful biological toxin.  It is a threat to our brains and nervous systems and our livers and our kidneys.  Too much exposure to methylmercury is likely to cause brain damage and nerve damage.

Fortunately, selenium supplements can help.  And they do help.  The relationship of mercury and selenium is a story with an ironic twist.  To the extent that selenium binds with mercury in the body and de-toxifies the mercury – a very good thing for us – to that extent the body is robbed of selenium that could be used for the production of beneficial selenoproteins with other important biological functions.

Protecting us against the toxic effects of mercury means fewer selenoproteins to act as antioxidants neutralizing harmful free radicals, fewer selenoproteins to strengthen immune system function and thyroid function, and fewer selenoproteins to help reduce the risk of cancer.

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