Tag: Fish

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Selenium and Mercury in the Fish We Eat

What should we know about eating fish and exposure to mercury in fish?
Fish and chips
Fish and chips. How careful should we be about eating fish? Which fish contain more harmful mercury than protective selenium? What should pregnant women know about eating fish during pregnancy?

Fact: Most fish contain mercury. Mercury is a toxic substance. Fortunately, most fish contain both selenium and mercury. On a molar basis, most edible fish contain more selenium than mercury. That makes it safe to eat most fish [Ralston 2024; Ralston 2016].

The selenium in fish binds tightly to mercury. The binding forms stable complexes that prevent mercury from damaging our cells. When there is more selenium than mercury (on a molar basis), this binding effectively neutralizes mercury’s toxicity. As a result, the mercury becomes biologically inactive and far less harmful when we eat the fish [Ralston 2023].

Even so, having just enough selenium available to neutralize the mercury exposure is not good enough. Logically, there must be a surplus of selenium. Without a surplus of selenium, there will not be enough selenium to synthesize antioxidant selenoenzymes. And, we need the antioxidant selenoenzymes to counteract the harmful free radicals in the brain. Providing more selenium, via supplementation if necessary, keeps selenoenzymes doing their antioxidant job. read more

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Selenium Protects Against Methylmercury in Fish

The health benefits of eating fish outweigh the health risks. This is especially true when we have sufficient dietary selenium intake and sufficient selenium status to 1) give a protective effect against methylmercury and 2) serve other biological purposes [Jorge 2024].

Salmon dinner contains selenium
Fatty fish such as herring, mackerel, and salmon are especially good sources of omega-3 fatty acids, protein, selenium, and vitamin D. Eating fatty fish regularly may reduce the risk of heart disease and stroke and enhance brain health.

To varying degrees, all fish contain some mercury. The mercury in fish and seafood is primarily in the form of methylmercury. Unchecked, the methylmercury targets the nervous system. It disrupts cellular processes. Too much exposure can lead to a loss of muscular coordination and to a loss in cognitive function. Accordingly, the presence of mercury could be a health risk for people who eat fish regularly [Jorge 2024].

Fortunately, many edible fish contain selenium in molar concentrations adequate to sequester the methylmercury in the fish and to render it less harmful. Ralston & Raymond have developed criteria for the calculation of selenium health based values. The calculations are based on the relative molar concentrations of mercury and selenium in various types of fish [Ralston 2016]. read more

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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]. read more