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Mercury damages the nervous system by blocking selenium’s numerous biochemical functions

- and that increases the need for selenium

Mercury damages the nervous system by blocking selenium’s numerous biochemical functionsSelenium is necessary for ensuring proper functioning of around 25 different enzymes – also known as selenoproteins – that are essential for energy turnover, metabolism, immune defense, fertility, and for antioxidant protection to help prevent cells and DNA from being damaged by oxidative stress. Selenium is also a so-called mercury antagonist that works by attaching itself to mercury, thereby preventing mercury’s harmful impact on the brain and nervous system. Once selenium has attached to mercury, however, it is no longer available to carry out all of its essential functions in the body. Because we are all exposed to mercury in some degree, this may cause a relative selenium deficiency that leaves our brain and nervous system particularly vulnerable to oxidative damage. In a new review article based on published research, Professor Nicholas V.C. Ralston and Dr. Laura J. Raymond explain why the toxic damage to the brain and nervous system is primarily a result of mercury’s inhibiting impact on the selenium metabolism. Selenium deficiencies are rather common, and mercury poisoning is an insidious problem, so the combination of these two problems deserves a lot more attention.

Mercury is a silvery liquid metal that produces several inorganic and organic compounds, which are toxic to humans. Everyone is exposed to mercury, which occurs in many different sources in the environment. The human fetus is particularly sensitive to this heavy metal. According to an EU report, mercury poisoning is a problem that costs Danish taxpayers close to DKr 750 million annually, mainly due to the expenses related to lowered IQ. What we see here, however, is just the tip of the iceberg, because mercury poisoning can cause a number of other symptoms. Therefore, it is essential to limit our exposure to this toxic metal. We must also focus on getting enough selenium, which offers protection against mercury. According to Professor Nicholas V.C. Ralston and Dr. Laura J. Raymond, the body’s selenium status is determining for the toxicity of mercury, and this has been strongly underestimated in numerous studies.

Mercury sources

  • Fossil fuels (especially coal)
  • Fish (especially predatory fish like tuna, hallibut, and shark)
  • Incineration plants, crematories, and church yards
  • Gold extraction
  • Amalgam fillings and wastewater from dental clinics
  • Electric bulbs, thermometers, and other types of measuring equipment
  • Certain vaccines (thimerosal)

Why is mercury so dangerous?

Mercury is chemically related to sulfur and selenium. Both sulfur and selenium are essential minerals, and our diet provides substantially more sulfur than selenium. Sulfurous molecules have an ability to transport mercury into the cells, where it disturbs or blocks many of the essential functions that are handled by selenoproteins.
Mercury can easily pass through the blood-brain-barrier and accumulate in the brain. It can also accumulate in the kidneys, in the thyroid gland, and in other organs that depend on the different selenoproteins. A human fetus is particularly vulnerable because of the rapid cell division and because selenium is essential for the development of the brain and the nervous system.
Moreover, mercury is a free radical source. Free radicals are highly aggressive molecules that can attack our cells. They are also a byproduct of our oxygen turnover, and our immune system even uses free radicals as a weapon in some of its defense mechanisms.
In other words, free radicals are a part of both essential and lethal processes and must therefore be kept on a tight leash, carefully controlled by antioxidants that prevent them from causing damage. Oxidative stress only occurs when the fine balance between free radicals and antioxidants is disturbed. Oxidative stress is the invisible enemy that eventually causes disease and deterioration.

Why our brain is particularly sensitive to mercury and oxidative stress

The human brain has an enormous energy turnover that is a result of handling millions of nerve transmissions. The brain alone consumes around 20 percent of the oxygen we breathe, so it automatically produces a large quantity of free radicals as a byproduct. The massive blood supply to the brain also harbors quite a lot of iron, which generates free radicals. Finally, mercury – as mentioned earlier – also generate cascades of free radicals.
The brain consists of approximately 60 percent fat. One of the most harmful effects of free radicals is when they attack polyunsaturated fatty acids in the cell membranes. This sets off a chain reaction that spreads from one cell to another like a bushfire. The phenomenon is known as lipid peroxidation. Free radicals can also attack and destroy enzymes, DNA, and other cell components, which means that oxidative damage to the brain can lead to structural and functional damage to brain cells and tissue.
Therefore, the brain needs a substantial amount of antioxidants to protect it against free radicals and oxidative stress. Selenium-containing antioxidants such as GPX (glutathione peroxidase 1-6) play a particularly important role that no other antioxidants can replace.

Different forms of mercury are found and accumulated through the food chain

Large quantities of mercury are released from incineration plants, power plants, and gold extraction processes. This produces mercury vapors that spread across borders to all parts of the world.
We breathe mercury, we get it from eating polluted fish, or we get exposed to the heavy metal through amalgam fillings and certain vaccines. Mercury is found in different forms. The oxidation of elemental mercury (Hg) produces water-soluble mercury forms that can spread to the environment when it rains or snows. Vertebrae are not able to take up these water-soluble mercury forms very easily, whereas anaerobe bacteria can methylate them and form methylmercury, which is highly toxic and accumulates through the food chain. Consequently, a fish at the top of the food chain can easily contain a million times more mercury than the water, in which is swims.

Different forms of mercury

  • Pure mercury (Hg)
  • Oxidized mercury (Hg+, Hg2+). Water-soluble forms that spread with vapors and rain
  • Methylmercury (CH3Hg+). Formed by bacteria. Bioaccumulates through the food chain.

Selenium is mercury’s biochemical target

According to Professor Nicholas V.C. Ralston and Dr. Laura J. Raymond, fish (from oceans and lakes) is the major dietary source of methylmercury. The ratio between mercury and selenium in the fish is determined by its place in the food chain. The more mercury that has accumulated through the food chain, the more selenium binds to the mercury, which reduces the amount of free (unbound) selenium in the fish. The body’s selenium reserves are a biochemical target for mercury. Mercury’s affinity to selenium is believed to be a million times higher than mercury’s affinity to sulfur.
Selenium binds to mercury by forming a compound called mercury selenide, which renders mercury harmless. Selenium therefore has a unique ability to bind mercury, but in doing so, selenium is no longer able to support the different selenium-dependent selenoproteins that are highly important for metabolic processes and protection against oxidative stress.

Eat fish from the lower part of the food chain

From a toxicological point of view, it is always safer to eat fish such as plaice, lemon sole, cod, haddock, hake, Pollock, herring, anchovies, and salmon, all of which belong to the lower part of the food chain, and where the selenium-mercury ratio is favorable.
On the other hand, Professor Ralston and Dr. Raymond say that one should avoid eating fish such as shark, swordfish, tuna, and halibut because this type of fish has an unfavorably balanced content of mercury and selenium. Health authorities generally advise children younger than 14 years and pregnant and/or lactating women to avoid eating predatory fish such as tuna and pike, and they recommend that hey stay away from canned tuna and albacore tuna. Children under the age of three years should not eat tuna at all, as their brains are still developing.

Pregnant woman should eat ”safe” fish and stay away of other predatory fish

Although fish is normally considered a good selenium source, it is important to check that there is a favorable balance between mercury and selenium. Pregnant women should pay extra attention. According to Ralston’s and Raymond’s new review article, it benefits the neurological development of children if their mothers have eaten eat “safe”, oily saltwater fish during pregnancy. The reason is that selenium is particularly important for brain development and protection of brain cells. Oily fish such as anchovies, herring, and salmon also provide rich quantities of essential omega-3 fatty acids, which are needed by the brain and nervous system. Pregnant women who choose not to stick with these “safe” fish types risk having babies with poorer health and different neurological disorders, mainly because of getting too little selenium and omega-3.

Danish and English research shows that mercury causes an increased risk of permanent brain damage in 25% of children. The damage impairs their cognitive skills.

Mercury poisoning is often insidious

Mercury can accumulate in different tissues, and there can easily be a delay between the ingestion of a harmful mercury dosage and the onset of the symptoms. A lot depends on how much selenium is in the body to begin with. Signs of mercury toxicity typically occur when the body’s selenium stores are empty. Exposure to mercury, especially with too little selenium to counteract it, may cause a number of different symptoms, as shown below. Nonetheless, people are very rarely controlled for mercury poisoning. There is also a risk that the diagnosis is not linked to the actual cause. Any treatment id therefore likely to draw out because the body is still poisoned by mercury.

Typical symptoms of mercury poisoning (where other causes have been excluded)

  • Tingling sensation in the lips and extremities
  • Thyroid disorders
  • Abnormal fatigue
  • Depression and fear
  • Headaches
  • Poor concentration
  • Impaired coordination
  • Speech difficulty
  • Impaired vision and deafness
  • Pain in muscles and joints
  • Frequent infections and inflammation
  • Metallic taste in mouth
  • Gum infection
  • Lower IQ (especially if the mother was diagnosed with poisoning during her pregnancy)
  • Death in the case of lethal doses

Treating acute mercury poisoning with large selenium doses

An otherwise healthy, 15-year-old male athlete, who weighed 70 kilos, was exposed to mercury vapors for several weeks. The patient had heart palpitations, elevated blood pressure, pain in the muscles, stomach, and testicles, insomnia, delusion, hallucinations, trembles, and lack of coordination. He lost 17 kilos, and hospital examinations revealed slightly elevated (23 µg/l) mercury levels that were still below the toxicity limit. The patient was treated with a chelating
drug named DMSA, but his condition continued to get worse.
They started treating him with supplements of selenium (500 µg daily), a therapeutic dosage that is around 10 times above the official recommendation for this micronutrient. The purpose was to saturate selenoprotein P, which functions as carrier in the blood, and to stimulate the synthesis of the GPX antioxidants. After three days, the patient felt substantially better. His heart palpitations stopped, and so did his delusions and stomach pain. Once he started eating a normal diet again, they were able to discharge him from hospital. The patient continued to take the selenium supplement, and after three months, all symptoms had practically vanished, except from the elevated blood pressure. After another two months, both his weight and blood pressure were back to normal, and he was able to resume athletics and football. The patient continued taking the large selenium dosage for eight months, but it did not result in elevated selenium levels in the blood. The selenium therapy simply showed that he still suffered from having too little selenium in the body, and that his body continued to use selenium to detoxify the body after being poisoned with mercury.

Signs of mercury poisoning are more likely to show in someone who lacks selenium

Why selenium deficiencies are so common

European farmland generally has a low selenium content, and there is also the fact that many of us eat very little fish and offal. Most Europeans have a daily selenium intake that is less than half of what experts recommend. Selenoprotein P is a very important selenium-containing protein that is used as a marker of the body’s selenium status. It takes around 100 micrograms of selenium daily to saturate selenoprotein P.

More information is needed about selenium’s protective effect against mercury

Besides the normal warnings against eating predatory fish, especially aimed at those who are pregnant, we need more official information about how to use selenium to counteract the toxic effect of mercury. This has been known since the 1960s and is shown in mammals, birds, and fish.

Compensating for the reduced selenium intake and reducing mercury toxicity

Selenium supplement are useful as compensation for the low selenium intake but can also be used for mercury detoxification. Organic selenium yeast that contains many different selenium species resembles a balanced diet with many different selenium sources.

Important selenium-containing compounds
Selenium-containing compound Function
Deiodinase type 1-3 Thyroid hormones
GPX 1-6 (Glutathione Peroxidase) Powerful antioxidants
Selenoprotein S Regulation of cytokines and inflammation response in cells
Selenoprotein P Antioxidant and selenium transport in the body
Selenoprotein R og N1 Antioxidants with several functions
Selenoprotein M Large amounts in the brain. Function not fully understood
Selenoprotein T Helps build cells and protein
TXNRD 1-3 Antioxidants, mitochondria, energy turnover, metabolism
MSRB1 Repair of oxidative damage
Even minor selenium deficiencies may result in selenoproteins not functioning optimally


Nicholas V.C. Ralston, Laura J. Raymond. Mercury´s neurotoxicity is characterized by its disruption of selenium biochemistry. 2018

Ralston,N., BBA- General Subjects (2018),

DR-dokumentar: De ufødte børn 03-11-2014

Niels Hertz: Selen – et livsvigtigt spormineral. Ny Videnskab 2002

Njord, V Svendsen: Næringsstoffer i fisk neutraliserer miljøgifte. 2012


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