Widespread selenium deficiency increases your risk of virus infections, thyroid disorders, impaired fertility, neurological disorders, cancer, and AIDS
Selenium is an essential trace element that is important for the immune defense, metabolism, fertility, nervous system, and cancer prevention. An estimated one billion people worldwide are believed to be selenium-deficient. Because European agricultural soil is low in selenium, we Europeans are more exposed than others. It appears that selenium deficiencies increase our risk of many acute, chronic, and life-threatening diseases, and the official recommendations for daily intake are too low, according to a new article about selenium deficiency, which is published in the scientific American database NCBI (National Center for Biotechnology Information).
Selenium was discovered in 1817 by a Swedish chemist named Jacob Berzelius. Selenium in large doses is toxic, and there are certain places on earth where the selenium concentration in the soil is high enough to be potentially lethal for humans and animals. For ages, selenium has had a bad and undeserved reputation. It was not until 1979 that it was discovered that selenium is an essential trace element for humans and animals.
What is all boils down to is getting the right amount of the nutrient, but climate change and nutrient depletion of the soil have increased the risk of selenium deficiency, especially in Europe and certain parts of Asia. Moreover, mercury poisoning, being infected with HIV plus other factors may increase your need for selenium. So why is selenium that important, and how much do we need for prevention and for treating various deficiency diseases?
Selenium’s importance for the function and protection of cells
In order to understand selenium’s role, we need to study the mineral at a cellular level. Selenium supports more than 25-30 different selenium-dependent enzymes that are also known as selenoproteins. Some selenoproteins influence our energy turnover and metabolism, some help the body break down waste products, some support the immune system, and some manage cell protection and cell repair. Selenoproteins are a natural elements of countless essential enzymes and antioxidants, on which our cells and tissues depend.
Over the past decades, studies of selenoproteins have shed light on a growing number of functions. It also turns out that many diseases that are caused by too little selenium may also be a result of having too little vitamin E, as vitamin E and selenium work as a pair.
The thyroid gland and selenium
The thyroid gland that is located in the anterior part of the lower neck produces two thyroid hormones called T3 and T4 (the number indicates how many iodine atoms the hormones contain). In order to activate the metabolism, a group of selenium-containing enzymes called deiodinases remove an iodine atom from T4, thereby converting it to active T3 hormone.
Another type of deiodinase is found in abundance in the central nervous system (CNS), in brown fat tissue, and in muscle tissue, where it is involved in the activation of the thyroid hormones. A third type of deiodinase is able to deactivate the thyroid hormones in order to prevent the metabolism from overheating.
Did you know that one in 10 Danes suffers from Hashimoto’s disease (slow metabolism) - often without knowing it?
Selenium-containing antioxidants provide outstanding protection of the body’s cells
Glutathione peroxidase (GPX) is a type of selenium-containing antioxidant that protects cells against oxidative stress, which is a condition with a disrupted balanced between free radicals and antioxidants. Free radicals are aggressive molecules that lack an electron. They are generated as a by-product of cellular oxygen metabolism, and the number of free radicals increases with inflammation, stress, poisoning, smoking, radiation, and ageing processes. The lipids (fats) in the cell membranes and our DNA are “sitting ducks” for free radical attacks, where the free radicals set off chain reactions inside and between the cells.
Free radicals are the culprits that set the stage for most chronic ailments. This is also the case with atherosclerosis: Cholesterol is an essential compound, and unless free radicals cause it to oxidize and become embedded in the blood vessel walls, it is totally harmless.
Glutathione peroxidase also belongs to the primary antioxidants, which no other antioxidants can replace. A selenium deficiency therefore makes cells extremely vulnerable to oxidative stress.
Glutathione peroxidase also works in collaboration with vitamin E in the prevention of atherosclerosis and in the protection of cell membranes, mitochondria, and DNA. Finally, there is the selenoprotein called MSRB1, which can repair oxidative damage.
Selenium-containing GPX antioxidants are found in all cells and have two functions:
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The immune defense, virus infections, and selenium
French doctors have conducted a study, in which they found that the selenium concentration drops rapidly during infections. Their experiment reveals that we humans use large quantities of selenium, when our immune system mobilizes its white blood cells.
In the northeastern Keshan province of China, where the selenium concentration in the soil is extremely low, scientists discovered, for the very first time, a potentially lethal heart disease, which is now named Keshan disease. It is caused by an otherwise harmless virus called the Coxsackie virus, which the immune defense is unable to fight without enough selenium. In 1965, the Chinese people in that province started to prevent and eradicate the disease by taking selenium supplements.
New strains of influenza typically originate from selenium-deprived parts of China. Influenza and other types of RNA virus tend to mutate when there is too little selenium. In other words, when the host immunity is weakened, the immune system is unable to recognize the virus and has to start all over again.
HIV (Human Immunodeficiency Virus) is also caused by an RNA virus, and AIDS mortality increases with decreasing selenium levels in the soil, according to an American study that looked at both factors in different states. Also, people survive longer with AIDS, when they have higher selenium levels in their blood.
Selenium evens has a protective role in patients with type B and type C hepatitis.
Selenium in the fight against virus infectionsSelenium strengthens the immune defense in several different ways and prevents virus from mutating. This is particularly important for preventing and fighting RNA virus that causes e.g. influenza, colds, herpes, HIV, Ebola, and Keshan disease. |
Neurological and psychiatric diseases
Studies show that selenium deficiency may lead to depressive and aggressive behavior. When the body lacks selenium, its first priority is to make sure that enough selenium reaches the brain, which shows how important the nutrient is for brain health. The human brain contains large quantities of selenoprotein M, a selenoprotein whose mechanism of action is still not clarified. However, it is known that the turnover of neurotransmitters depends on selenium, and the selenium-containing antioxidant, glutathione peroxidase, protects the nerve cells and supportive cells of the brain. One study demonstrated that Alzheimer’s patients only had about 60 percent as much selenium as healthy controls.
Fertility, sperm cells, and selenium
Selenium is important for the synthesis of testosterone and for the formation of healthy sperm cells, which are extremely vulnerable to oxidative stress. Research shows that in around 50% of childless couples, the protection of the man’s sperm cell DNA is compromised, and that may cause something known as DNA fragmentation. Even though the sperm cells are technically able to swim, the sperm cell that reaches the egg first may not necessarily be the most fit for the job. In other words, the sperm cell is able to fertilize the egg, but if its genetic payload (DNA) is damaged, the egg will not be able to develop normally and will soon be expelled.
Therefore, sperm cells and their DNA must be protected against free radicals and oxidative stress with help from antioxidants such as glutathione peroxidase.
Supplements of selenium yeast make both pregnancy and birth safer
Studies suggest that selenium has a supportive and protective role during pregnancy. Daily supplementation with 100 micrograms of selenium yeast from the first trimester until delivery may help the expecting mother lower by 30 percent her risk of a ruptured fetal membrane, according to a placebo-controlled study that is published in Journal of Obstetrics and Gynaecology.
Pregnant study participants that took supplements of selenium yeast also had a lower rate of preeclampsia, which is the second-most common cause of premature delivery. Preeclampsia may also cause life-threatening conditions such as eclampsia.
Inflammation
Chronic inflammation is the common thread of most chronic diseases, even those that go unnoticed. Selenoprotein S regulates inflammatory processes in the endoplasmic reticulum of the cells, which is important for many different metabolic processes in the cell.
A Portuguese study from 2014 showed that lack of selenoprotein S is involved in an increased number of different cytokines, which are relevant for inflammation and Hashimoto’s disease.
Cancer
Selenium helps the immune system fight cancer in a number of different ways, it prevents oxidative stress and inflammation, and it repairs cell damage. In 1996, an American scientist named Larry Clark documented with his NPC study (Nutritional Prevention of Cancer) that daily supplementation with 200 micrograms of selenium yeast that contains around 30 different organic selenium species lowers the risk of cancer and cancer-related deaths by around 50 percent.
Because it often takes several years for cancer to develop, selenium seems to play a role in long-term prevention. For instance, it has was observed in studies that both American and Japanese women with breast cancer had lower selenium concentrations in their blood compared with healthy female controls long before the cancer developed.
Danish scientists from the University of Copenhagen have uncovered how the selenium compound methylselenol prevents cancer cells from spreading as a result of cellular stress and a derailed immune defense. According to a study from the Technical University of Denmark, daily supplementation with 200 micrograms of selenium yeast lowers the risk of prostate cancer. Larger concentrations of selenium in the blood are associated with a lower risk of cancer in the colon and liver, according to a 2017 study that was headed by Dr. David Hughes from the Conway Institute, University College in Dublin.
Over the past decades, a number of studies have looked at selenium’s different anti-cancer mechanisms. It appears that the result of these studies depends, to a great extent, on how much selenium is in the soil to begin with, and what form of selenium people take as a supplement. Selenium yeast has been shown to have the best effect, whereas selenomethionine appears not to work all that convincingly.
Selenium neutralizes mercury
Mercury is one of the most harmful environmental toxins. It accumulates in the brain, kidneys, thyroid gland, and other organs. Large amounts of mercury are released into the environment from incineration plants, power plants, and gold mining that causes mercury vapors to spread across country borders to different parts of the world.
We breathe in mercury, we get it from eating polluted fish, and we are exposed to the harmful heavy metal from amalgam fillings and certain vaccines.
Scientists have discovered that selenium has a special affinity for mercury and binds it to form mercury selenide, an inert compound that is harmless to humans. Once selenium has formed a bond with mercury, the selenium is no longer available to support all the essential selenoproteins. Because we are all exposed to mercury to some degree, we may easily develop a relative selenium deficiency, to which our brain and nervous system are particularly vulnerable.
According to Professor Nicholas V. C. Ralston and Dr. Laura J. Raymond, fish is the primary source of dietary mercury, especially predatory fish like tuna, halibut, and shark. It is therefore safer to eat plaice, cod, herring, anchovies, and salmon, all of which are examples of fish from the lower part of the food chain, where the selenium-mercury ratio is more favorable for our health (less mercury and more selenium).
Mercury is able to
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Enriching artificial fertilizers with selenium
As mentioned earlier, the selenium content in agricultural soil is low. This used to be a particularly big problem in Finland, where blood analyses showed that the population had very low selenium levels. Because there was a high rate of cardiovascular disease, the Finnish government decided in the 1980s to add selenium to artificial fertilizers. This affected selenium levels throughout the food chain and resulted in a comparatively swift improvement of the Finns’ selenium status.
Domestic animals get selenium, and humans belong to the same food chain
Since 1975, farmers in Denmark have given selenium to pigs and cattle to prevent a variety of deficiency diseases such as impaired fertility, joint inflammation, and heart attack. Even dog food contains extra selenium. We humans belong to the same food chain, but even though farmers have made it a habit to give extra selenium to the animals, a lot of humans get too little.
Where is selenium found – and how do I get enough?
Some of the best selenium sources are fish, shellfish, offal, eggs, dairy products, Brazil nuts, shiitake mushrooms, and green vegetables. Many scientists recommend a daily selenium intake of around 100 micrograms, which is the amount that is needed to fully saturate selenoprotein P. This selenoprotein works by transporting selenium to all the different tissues, and it is a useful marker of the body’s selenium status. The average European diet is believed to provide as little as 50 micrograms of selenium, or less.
Although fish and shellfish are considered to be good selenium sources, research shows that even if you consume seafood five days a week, you don’t get enough selenium to effectively saturate selenoprotein P. The study was conducted by Danish scientists in collaboration with the Danish Cancer Society.
In many other countries such as the United States and Canada, the natural selenium intake from the diet lies in the range of 100-200 micrograms due to the higher selenium content in the soil.
| Selenium yeast with many different selenium compounds is the best way of getting the same variety of selenium species as what you would get from eating a balanced diet with many different selenium sources. |
Toxicity and upper safe limit
The European Food Safety Authority (EFSA) has established an upper safe intake limit for selenium at 300 micrograms per day, while WHO has set the upper safe limit at 400 micrograms.
Signs of poisoning are normally seen with daily intake of around 800-1,000 micrograms. These symptoms, which typically include headache, tiredness, dizziness, stomach pain, constipation, and nausea, are transitory. Rashes, brittle hair and nail deformities are only seen in rare cases. In the case of extremely toxic selenium doses, selenium is excreted via the lungs, which may result in a noticeable garlic-like breath. In worst case, selenium toxicity can cause paralysis.
Adults are normally able to tolerate acute selenium doses of up to 10 mg, but there is no reason to overdose on the mineral. What is important is to get enough selenium to saturate the vital selenoproteins.
| Important selenium-dependent proteins | |
| Selenoprotein | Function |
| Deiodinase type 1-3 | Thyroid hormones |
| Glutathione peroxidase, GPX 1-6 | Powerful antioxidants |
| Selenoptotein S | Regulation of cytokines and inflammatory response in cells |
| Selenoprotein P | Antioxidant and selenium transport |
| Selenoprotein R and N1 | Antioxidants with several other functions |
| Selenoprotein M | Large concentrations in the brain. Function not yet fully understood |
| Selenoprotein T | Involved in cell structuring and proteins |
| TXNRD 1-3 | Antioxidants, mitochondria, energy turnover, metabolism |
| MSRB1 | Repair of oxidative damage |
| Even a minor selenium deficiency may result in suboptimal functioning of all the different selenoproteins | |
References:
Aparna P. Shreenath; Jennifer Dooley. Selenium, Deficiency. NCBI October 27, 2018
Jones GD et al. Selenium deficiency risk predicted to increase under future climate change. Proceedings of the National Academy of Sciences 2017
Editorial team. Selenium deficiency promoted by climate change. ETHzüric 2017
Hilten T Mistry et al. Selenium in reproductive health. Journal of Obstetrics and Gynaecology. 2011
Fatemeh Tara et al. Selenium Supplementation and the Incidence of Preeclampsia in Pregnant Iranian Women: A Randomized, Double-Blind, Placebo-Controlled Pilot Trial. Taiwanese Journal of Obstetrics and Gynecology. 2010
Fatemeh Tara et al. Selenium supplementation and premature (pre-labor) rupture of membranes: a randomized double-blind placebo-controlled trial. Journal of Obstetrics and Gynaecology. 2010
Nicholas V.C. Ralston, Laura J. Raymond. Mercury´s neurotoxicity is characterized by its disruption of selenium biochemistry. 2018
Malene Outzen et al. Selenium status and risk of prostate cancer in a Danish population. British Journal of Nutrition 2016
Hagemann-Jensen Michael et al. The Selenium Metabolite Methylselenol Regulates the Expression of Ligands That Trigger Immune Activation through the Lymphocyte Receptor NKG2D. The Journal of Biological Chemistry. 2014.
New Links between selenium and cancer prevention. HRB. December 2017
Clark LC et al: Effects of Selenium Supplementation for Cancer Prevention in Patients with Carcinoma of the Skin. JAMA: 1997.
Klein EA et al. Vitamin E and the risk of prostate cancer: The Selenium and Vitamin E Cancer Prevention Trial (SELECT). JAMA 2011.
Lutz Shomburg. Dietary Selenium and Human Health. Nutrients 2016
