{"id":794,"date":"2017-11-14T06:59:57","date_gmt":"2017-11-14T06:59:57","guid":{"rendered":"http:\/\/seleniumfacts.com\/?p=794"},"modified":"2017-11-21T11:59:39","modified_gmt":"2017-11-21T11:59:39","slug":"selenium-mercury-eating-fish","status":"publish","type":"post","link":"https:\/\/seleniumfacts.com\/index.php\/selenium-mercury-eating-fish","title":{"rendered":"Selenium and mercury and eating fish"},"content":{"rendered":"
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Ocean fish \u2013 salmon, herring, mackerel, and sardines \u2013 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.\u00a0 Whatever mercury there is in these fish has bound with the selenium in the fish. \u00a0 This chemical binding has rendered the mercury harmless but has also depleted the amount of selenium available for absorption.<\/strong><\/figcaption><\/figure>\n

Too many of us are missing out on the health benefits of the omega<\/em>-3 fatty acids available to us from eating certain types of fish a couple of times a week.\u00a0 Why are we avoiding fish?\u00a0 Because many of us are afraid of \u201ceating mercury\u201d in the fish.<\/strong><\/p>\n

It turns out, there is research to show that this is a misconception.\u00a0 Professor Nick Ralston and his colleagues at the University of North Dakota\u2019s Energy and Environmental Research Center have measured and evaluated the molar ratios of selenium in fish to the mercury in fish [Ralston 2007, 2016].<\/strong><\/p>\n

Their studies show that many of the edible ocean fish have an abundance of selenium in relation to mercury.\u00a0 So, not only are we missing out on the omega<\/em>-3 fatty acid benefits, we are also missing out on a good source of dietary selenium [Berry 2008].<\/strong><\/p>\n

Here is what Dr. Ralston says happens in many varieties of ocean-caught fish.\u00a0 The mercury in the fish preferentially binds with the available selenium in the fish and is rendered harmless [Ralston 2010]. \u00a0 In doing so, however, the mercury depletes the amount of selenium available to us for the bio-synthesis of needed selenoproteins.<\/strong><\/p>\n

So the real problem is a problem of selenium depletion more than it is a problem of mercury intoxication.<\/strong><\/p>\n

Let’s examine the question of eating ocean-caught fish step-by-step.<\/strong><\/p>\n

First: Where does the mercury in fish come from?<\/strong>
\nLarge concentrations of the neurotoxin mercury in edible ocean fishes are essentially a man-made problem.\u00a0 We release great quantities of mercury into the atmosphere from power plants and industrial plants that burn fossil fuels such as coal and oil.\u00a0 The mercury falls onto the oceans (as well as onto lakes and rivers).\u00a0 Plankton and other forms of sea life take on the mercury, and the mercury spreads up the food chain as the larger fish eat the smaller fish.<\/p>\n

We humans not only breathe in the mercury in the air.\u00a0 If we eat the wrong kinds of fish, we also eat the concentrated mercury in fish and seafood.\u00a0 Too much exposure to mercury will cause brain and nervous system damage and developmental problems for humans.\u00a0 However,<\/em> if the mercury is bound together with selenium <\/a>in the fish, it will cease to be harmful to humans [Ralston 2010].<\/p>\n

Second: What is the role of selenium in in our bodies?<\/strong>
\nWe need selenium for the formation of selenoproteins (= proteins containing selenium incorporated into the amino acid selenocysteine).\u00a0 These selenoproteins, many of which act as antioxidant enzymes, are necessary to protect the brain and the nervous system as well as other body systems from oxidative damage.\u00a0 The body needs a continuing supply of dietary or supplemental selenium to synthesize the selenoproteins that protect against oxidative damage.<\/p>\n

Third: How does selenium prevent oxidative stress and damage?<\/strong>
\nNormal everyday oxygen-dependent metabolism in the body as well as exposures to environmental toxins and radiation produce oxygen reactive species, also known as free radicals.\u00a0 The condition of oxidative stress<\/em>, usually a bad condition for us humans, is defined as an imbalance of the numbers of these harmful free radicals and the numbers of antioxidants needed to neutralize the free radicals.<\/p>\n

Oxidative damage<\/em> is the resulting damage to cells and tissues and DNA and lipoproteins that is caused by chain reactions of these reactive oxygen species.<\/p>\n

Selenium-dependent antioxidants<\/a> such as the glutathione peroxidases, the thioredoxin reductases, and the selenoprotein P prevent and even reverse the oxidative damage in the brain and nervous systems and in other body systems.<\/p>\n

From this brief description, we see that a lack of selenium for the formation of the antioxidant selenoproteins will have a deleterious effect on human health.\u00a0 Mercury’s binding with selenium reduces the amount of mercury we get from eating fish but also reduces the amount of selenium available to us from fish.<\/p>\n

Fourth: How does selenium disarm mercury?<\/strong>
\nMercury, in the common form of methylmercury, is a toxic agent in fish and in humans.\u00a0 Methylmercury molecules have a great affinity for binding with selenium<\/a> in the fish and also in humans.\u00a0 Mercury has up to one million times more affinity for binding with selenium than with sulfur, the second most common substance with which mercury forms chemical bonds.<\/p>\n

Fifth: What is the good and the bad of mercury\u2019s binding with selenium?<\/strong>
\nIn an organism, fish or human, when there is selenium and there is mercury, the mercury will bind with the available selenium, tying the selenium up irreversibly in protein complexes.\u00a0 Mercury sequesters<\/em> the selenium, so to speak.<\/p>\n

This is both good and bad.<\/p>\n

On the one hand, \u2013 the good side \u2013 the ingested methylmercury is inhibited from having toxic effects of its own.\u00a0 It is bound up with the selenium in the protein complexes and is deactivated.<\/p>\n

On the other hand, \u2013 the bad side \u2013 the selenium is also bound up and is no longer available for the formation of the essential antioxidant selenoproteins.<\/p>\n

As a result, more oxidative stress and oxidative damage occur.\u00a0 There are not enough selenium-dependent selenoproteins available to stop the damage.<\/p>\n

Sixth: Can we eat some varieties of ocean fish?<\/strong>
\nFortunately, many edible varieties of ocean fish have high selenium-to-mercury ratios.\u00a0 There is more than enough selenium in these fish to bind with the mercury and still have some selenium left over when we eat fish.\u00a0 There is still a little selenium for the synthesis of selenoproteins.<\/p>\n

But, notice, there is not as much selenium available as there would be if there were not much mercury in the tissues of the fish.\u00a0 Mercury is a big depleter<\/em> of the selenium available for selenoproteins to be formed.<\/p>\n

Seventh: What are Dr. Ralston\u2019s Selenium-related Health Benefit Value calculations?<\/strong>
\nDr. Ralston\u2019s selenium-related health benefit value calculations <\/a>are intended for use as a risk assessment tool.\u00a0 The calculations are based on the molar concentrations of selenium and methylmercury in various types of fish.\u00a0 The more favorable the ratio of selenium to methylmercury in the fish, the more benefit and the less risk there is in eating the fish [Ralston 2016].<\/p>\n

Eighth: Fish for pregnant and breastfeeding women<\/strong>
\nThe selenium-related health benefit values are important not just for the general public but also, especially, for pregnant and breastfeeding women.\u00a0 Which fish should they avoid?\u00a0 Which fish should they eat?<\/p>\n

Methylmercury can cross the placental and blood-brain barriers, so too much mercury during pregnancy can affect the brain development of the fetus.<\/p>\n

At the same time, a lack of selenoproteins can also affect the brain development of the fetus<\/a> [Gilman 2015].<\/p>\n

Mothers\u2019 eating the right kinds of fish every week, fish with high selenium-to-mercury ratios, can help to improve the brain development of infants.\u00a0 Fish is a good source of omega<\/em>-3 fatty acids, protein, many vitamins and minerals, and the important trace element selenium.<\/p>\n

Ninth: Which ocean fish have high amounts of selenium?<\/strong>
\nThe question is, which ocean fish can be safely eaten, and which ones cannot?<\/p>\n

Here is a partial list of ocean fish that have high selenium-to-mercury ratios:<\/p>\n