Tag: Mercury toxicity

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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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Mercury’s neurotoxicity and disruption of selenium biochemistry

The brain is particularly vulnerable to oxidative damage in the absence of adequate antioxidant selenoprotein protection for a variety of reasons: the brain has limited antioxidant enzyme pathways, the brain has high iron content, and the brain contains many long-chain polyunsaturated fatty acids, which are vulnerable to lipid oxidation. Oxidative damage to the brain results in structural and functional damage to brain cells and tissues. A selenium yeast supplement has proven effective at reducing the levels of bio-markers of lipid peroxidation and oxidative damage to DNA. An exclusively selenomethionine supplement was not effective [Richie 2014].
Selenium containing antioxidant selenoproteins play an important role in the prevention and reversal of oxidative damage in the brain.  This role has generally been underestimated in studies of the toxicity of elemental mercury and methylmercury.  The common understanding has been that selenium helps to prevent mercury toxicity by binding with mercury and rendering the mercury inactive.

This chemical binding and inactivation of mercury does take place.  Mercury has a great affinity for selenium, estimated to be approximately one million times stronger than mercury’s affinity for sulfur.  So, selenium’s binding with mercury in the tissues does keep the mercury from getting into mischief in the brain and spinal cord, peripheral nervous system, and endocrine system. read more