Tag: Mercury

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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 and Mercury Toxicity

Nick Ralston has spent many years doing research into the interaction between selenium and mercury in the human body. He is a research scientist and adjunct professor in the Department of Earth System Sciences and Policy at the University of North Dakota. His research has changed how scientists and regulators think about mercury’s impact on human health. Now, scientists regard selenium status as a central factor in determining the risk of mercury toxicity [Ralston 2018; Ralston 2010].

Selenium basic facts
Selenium and mercury interact strongly with one another. Selenium can bind to mercury and protect brain from damage. However, mercury’s binding to selenium reduces the amount of selenium available for antioxidant defense and thyroid function.

Previously, the most common explanation of mercury toxicity was that mercury exposure directly caused oxidative stress. Selenium’s binding with mercury, it was thought, reduced the risk of oxidative stress and reduced the risk of mercury toxicity. 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 Toxic Metals and the Ageing Kidney

In individuals older than 50-60 years, the kidneys’ glomerular filtration rate decreases with increasing age. The glomerular filtration rate is a measure of how well your kidneys are working. In your kidneys, there are tiny filters (called glomeruli) that remove waste and excess fluid from the blood.

Jan Aaseth
Jan Aaseth is a Norwegian physician and professor who has done extensive research in endocrinology, toxicology, and medical biochemistry. Here we summarize his review of the relationship between selenium status, heavy metal toxicity, and the kidneys.

Exposure to toxic metals – mercury, cadmium, lead – can be detrimental to kidneys of normal adults. Accordingly, exposure to toxic metals can affect individuals with reduced glomerular filtration rates even more adversely.

Professor Jan Aaseth and a team of researchers have reviewed the available research data. Their findings show the following relationships [Aaseth 2021]:

Elderly Individuals More Susceptible to Toxic Metal Exposure

Healthy elderly individuals are capable, for the most part, of maintaining normal kidney function. However, especially after the age of 70 years, physiological changes occur in the kidneys. read more

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Selenium, Fish, and Mercury: Important Facts

Fish should be an important part of our diets. Professor Nick Ralston at the University of North Dakota has drawn our attention to the webpages entitled Fish, Mercury, and Nutrition: The Net Effects. The URL is http://net-effects.und.edu/factsheets.aspx

The Cover of the Fish, Mercury, and Nutrition brochure
The Fish, Mercury, and Nutrition webpages contain fact sheets, a documentary video, video clips, and links to informative websites.

On these webpages, Professor Ralston and his colleagues explain why the benefits of regularly eating fish, especially ocean fish, are often overlooked. Too many of us have cut back on our fish consumption because we have been worried about exposure to toxic mercury.

However, we have been receiving insufficient information about the relative benefits and risks of eating ocean fish. In fact, our avoiding fish meals may be having negative health consequences in some cases. read more

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Selenium and Mercury Toxicity

A plate of salmon.
Eating fish will give pregnant women and children selenium and other nutrients that will promote the children’s growth and development. Eating fish may give adults heart health benefits. However, some ocean fish contain more mercury than selenium and should therefore be avoided. Consequently, the US Food and Drug Administration advises against eating meals from predatory whales, sharks, swordfish, king mackerel, marlin, orange roughy, tilefish, and big-eye tuna. Most other ocean fish will have more selenium than mercury in their tissues and should be safe, even advisable, to eat.

The selenium in our cells is the molecular “target” of toxic mercury. Inhibition of the normal biological activity of seleno-enzymes is the mechanism by which mercury damages our cells, most particularly our brain and nerve cells [Ralston & Raymond 2018].

Conceiving of selenium as the “target” of mercury leads to a better understanding of mercury toxicity than the old theory of selenium as the “tonic” that binds toxic mercury in a form that is no longer harmful [Ralston & Raymond 2018].

Professor Nicholas Ralston and consultant Lisa Raymond have done a review of the research literature about the characteristics of mercury toxicity to identify the selenium-dependent aspects of mercury’s biochemical mechanisms and effects. Their conclusions [Ralston & Raymond 2018]: read more

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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. read more