Are you getting enough of the essential nutrient selenium?

It is estimated that one billion people worldwide lack selenium. This has fatal consequences for public health because it increases the risk of virus infections, thyroid disorders, cardiovascular diseases, cancer, neurological disorders, and involuntary infertility. Adding to that problem is the fact that mercury, a known environmental toxin, throws a wrench into selenium’s different functions. In the following, we have compiled a long list of studies that look closer at the consequences of selenium deficiency and the advantage of optimizing the body’s selenium status with help from supplements.

Selenium was discovered in 1817 by the Swedish scientist Jacob Berzelius. The element is named after the Greek moon goddess, Selene. It was first believed that selenium was a toxic mineral. It wasn’t until 1979 that science finally established that selenium is one of the essential minerals that are vital for humans and animals in the exact right amounts.
Selenium supports a host of different selenoproteins that are of importance to:

• Cellular structure
• Control and activation of numerous genes and micro-RNA
• Energy metabolism and utilization of coenzyme Q10
• Immune system and inflammatory processes
• Activation of thyroid hormones
• Antioxidants such as glutathione peroxidase (GPS) that neutralizes free radicals

Even minor selenium deficiencies prevent the selenoproteins from functioning optimally. The body always gives first priority to its energy turnover, which sequesters selenium that is otherwise needed for a variety of other functions like the immune defense, thyroid function, nervous system, fertility etc. The relative selenium deficiency also makes cells increasingly vulnerable to oxidative stress and inflammation, which may cause infections to become dangerous. This the common thread of many chronic ailments.

Widespread selenium throughout the entire food chain

Our dietary selenium intake hinges on the natural selenium content in the soil. This can vary substantially from one part of the world to another – sometimes by several hundred percent. Over 40 countries are reported to have selenium-depleted agricultural soil. The lowest levels have been observed in Europe, large parts of China, South America, India, Africa, and the Southwestern regions of the United States. What makes matters even worse is intensified farming that depletes selenium levels even more. This can be seen throughout the entire food chain. It is estimated that around one billion people worldwide lack selenium. The problem requires immediate attention, exactly like we have solved iodine deficiencies by introducing iodine-enriched table salt.
In Denmark, it has been common practice since 1975 to feed extra selenium to livestock in order to prevent deficiency diseases like impaired fertility, joint inflammation, and heart attacks. Even pet food has selenium added to it. Healthy animals equal a healthy bottom line.

Solving the selenium problem in China and Finland

In China, the selenium content in the soil varies a lot. In the Keshan province in the north-eastern part of China where the soil is extremely low in selenium, a potentially lethal heart disease named Keshan disease was discovered for the first time. The disease was caused by an otherwise harmless virus called coxsackie, a virus that the immune defense is unable to fight without the presence of selenium. As early as in 1965, the Chinese population in that area set out to prevent and eradicate the feared disease by using selenium supplements. Still, China still hast vast areas with selenium-depleted soil, which increases the risk of a number of different deficiency diseases.
The agricultural soil in Finland is also low in selenium. In the mid-1980s, Finland (as the only European country) introduced mandatory selenium-fortification of fertilizers as a way to prevent deficiency diseases. The average Finnish selenium intake today is around 100-110 micrograms, which is considered adequate. This simple adjustment turned out to have a positive impact on public health and on the rate of cardiovascular diseases.

Selenium for the immune defense and for protection against virus infections

Our immune defense is able to tackle nearly all types of germs and infections without us noticing. Selenium is highly relevant for the formation and the activity of macrophages as part of the innate immune defense and for T cells in the adaptive immune defense. This includes the communication between immune cells that is essential for swift and effective immune reactions.
Selenium is particularly important for our ability to fight off virus infections in the respiratory tract. At the same time, the selenium-containing GPX antioxidants protect the body against oxidative stress, which can otherwise cause damage to healthy tissue. In addition, selenium prevents viruses from mutating and becoming increasingly dangerous.
The selenium levels in blood drop drastically in connection with infections. This is because so much selenium is needed for the immune system and the body’s antioxidant defense. If there is too little selenium in the body, it increases the risk of infections and complications in connection with influenza and virus infections.
An older study of HIV-infected patients showed that those with low selenium concentrations in the blood had fewer T helper cells, more rapid progression of AIDS, and a 20 percent higher risk of dying of their disease.
In 2020, the British selenium scientist Margaret Rayman observed a link between soil selenium levels and the risk of dying of COVID-19 (SARS-CoV-2). And a German study has shown that patients who survive COVID-19 have higher selenium levels in the blood compared with healthy controls. In a review article from 2021 (Qiyuan Liu et al.), Chinese scientists pored over multiple studies of selenium’s role in the prevention and treatment of infections caused by different types of viruses such as HIV, Ebola, coxsackie, influenza, and COVID-19, all of which have a formidable ability to mutate.
According to an American study, daily supplementation with 200 micrograms of selenium increases blood cell activity by as much as 80 percent.

Selenium and cardiovascular disease

Atherosclerosis and cardiovascular disease are still the leading causes of death. Atherosclerosis is caused by deposits of oxidated LDL cholesterol, calcium, and fat on the inside of the arterial walls. This narrows the inside circumference and makes it more difficult for blood to circulate. In that case, cholesterol, which is otherwise essential, oxidizes and turns into a health threat. The oxidation is caused by oxidative stress, which is when harmful free radicals outnumber the protective antioxidants.
Over the past decades, numerous studies have shown that selenium deficiency increases the risk of blood clots and sudden cardiac death. Research also shows that selenium supplementation protects against atherosclerosis, mainly because selenium supports the powerful GPX antioxidants that protect against oxidative stress. In the groundbreaking KiSel-10 study, supplements of selenium yeast were given together with coenzyme Q10 to a large group of healthy seniors. The combination of these two nutrients is crucial because the body’s endogenous Q10 production, which is important for energy turnover, heart function, and circulatory health, decreases with age, and selenium bolsters the effect of Q10.
Every day, one group got 200 mg of Q10 and 200 micrograms of pharmaceutical-grade selenium yeast, while the other group got matching placebo. After five years, the group that got active supplements had 54% lower cardiovascular mortality, increased heart muscle strength, and improved quality of life, compared with the placebo group. Follow-ups after 10 and 12 years showed that those who had taken selenium and Q10 had a significant long-term effect on heart function and longevity.

Selenium and thyroid diseases

The thyroid gland contains more selenium than any other bodily tissue and is the gland that produces two different thyroid hormones:

• T4 (passive) – contains four iodine atoms.
• T3 (active) – contains three iodine atoms.

In order to activate the metabolism in the different tissues, a group of selenium-containing proteins (deiodinases) remove an iodine atom from T4, thereby converting passive T4 into active T3. This is done in step with the body’s need for T3. The selenium-containing GPX antioxidants also protect the extremely active thyroid gland against oxidative stress.
Around half a million Danes are believed to suffer from Hashimoto’s thyroiditis, an autoimmune disease that causes the metabolism to slow down (hypothyroidism). The majority has not even been diagnosed yet and many are treated with synthetic T4 hormone and end up feeling worse, ironically. Graves’ disease, another autoimmune thyroid disorder, causes the metabolic rate to speed up (hyperthyroidism). This condition is treated with antithyroid drugs, surgery, radioactive iodine, and corticosteroids that are known to cause side effects.
Both iodine and selenium are important in the prevention of thyroid disorders. For some reason, there is only focus on iodine, which is added to table salt.
Multiple studies show that daily supplementation with 200 micrograms of selenium given to patients with autoimmune thyroid disorders has a positive effect in the course of 3-6 months. In patients with Hashimoto’s and in pregnant women with early stages of the condition (seen by the presence of anti-TPO antibodies), supplementation with selenium has been shown to:

• Improve quality of life
• Lower levels of anti-TPO (a sign of less inflammation)
• Improve the structure of the thyroid gland

Two large Danish studies (CATALYT and GRASS) show that daily supplementation with 200 micrograms of selenium yeast helps thyroid patients who fail to benefit from their medical therapy.

Selenium and cancer

Cancer includes a long list of different diseases that involve uncontrolled, malignant cell growth. Many years often pass from the time of the initial cell change until a tumor is discovered. It is commonly known that tobacco, processed meats, alcohol, and UV radiation increase the risk of cancer. But even people who follow the guidelines for good health can contract cancer. One contributing factor that may be an overlooked problem is lack of selenium because it can be difficult to get enough selenium from your diet. Several large-scale studies have revealed differences in levels of selenium in blood or nail tissue in cancer patients and healthy controls long before the disease is discovered. It is therefore important to make sure to get plenty of selenium throughout life, mainly because the nutrient has the following anti-cancer properties:

• It controls and activates countless genes and micro-RNA
• It regulates cell growth
• It supports powerful GPX antioxidants that protect cells and their DNA and mitochondria against free radicals
• It repairs DNA damage
• It prevents new blood vessels from forming in tumors (anti-angiogenesis)
• It helps diseased or malfunctioning cells to self-destruct (apoptosis)
• It contributes to a well-functioning immune system
• It counteracts inflammation
• It neutralizes environmental toxins such as mercury

Decades of research in Denmark and abroad has shown a clear link between selenium deficiency and common cancer forms. In 1977, Professor Schrauzer published studies that revealed an inverse relation between selenium intake and cancer mortality in 27 different countries. In 1996, Professor Larry Clark, a renowned scientist, documented that daily supplementation with organic selenium yeast lowered the risk of several common cancer forms and reduced overall cancer mortality by around 50 percent. Among the selenium-supplemented participants, there were 63 percent fewer cases of prostate cancer, 58% fewer cases of colorectal cancer, and 46% fewer cases of lung cancer. The later SELECT study, however, did not produce a similar result, but that stands to reason. The study participants already had high selenium levels in their blood. Moreover, this study used selenomethionine and synthetic vitamin E. It is always important to look at the type and quality of the supplements used in such studies because it can affect the outcome.
In prostate cancer, carcinoma, and certain types of leukemia, the cells produce an excessive amount of NKG2D ligands that cause cellular stress and an overactive immune defense. According to Danish researchers, methyl selenol counteracts both the uncontrollable production of NKG2D ligands and their overrepresentation in the bloodstream.
A meta-analysis has shown a link between prostate cancer and selenium deficiency, and a study from the Technical University of Denmark shows that daily supplementation with 200 micrograms of selenium yeast lowers the risk of prostate cancer.
Luigina Bonelli, an Italian scientist, has demonstrated in a study that selenium plus zinc and certain other antioxidants protect against colorectal adenomas, a type of polyps that can turn into bowel cancer. Supplementing with these nutrients also has a long-term protective effect.
Swedish breast cancer patients with low blood levels of selenium, selenoprotein P, and GPX are 50 percent more likely to die of breast cancer after eight years compared with patients that have adequate levels of the mentioned variables in their blood. The study supports earlier Swedish research.
A Polish population study has shown that higher blood selenium levels increase the chances of 10-year breast cancer survival. An analysis of earlier studies has shown that having higher levels of selenium in the blood is linked to a lower risk of developing bladder cancer.

Selenium and fertility

Selenium is crucial for male and female fertility, and selenium deficiency is a contributing (and overlooked) factor in the widespread problems with involuntary childlessness. Selenium plays a key role in the formation of healthy sperm cells, and low dietary selenium intake may impair both sperm cell quality and motility. Selenium-containing antioxidants protect sperm cells against oxidative stress. Therefore, having too little selenium in the body may result in damage to the sperm cell DNA (DNA fragmentation). This means that even if a sperm cell fertilizes an egg successfully, the egg will not mature normally and will be rejected.
A study of Mexican children has shown that lack of selenium is associated with delayed development of pubic hair and sex organs in boys. Mexican scientists have also observed that supplementing with selenium, zinc, Q10, and omega-3 fatty aids has a positive influence on the quantity and quality of sperm cells.
Selenoproteins are also important for fetal development and protection against oxidative stress. Lack of selenium during pregnancy may result in stunted fetal growth and low birth weight. Daily supplementation with 100 micrograms of selenium yeast from the first trimester until delivery helps lower the risk of a ruptured fetal membrane by around one third. Pregnant women who took supplements of selenium yeast had a lower rate of preeclampsia, which is the most frequent cause of premature delivery. Preeclampsia may also cause life-threatening eclampsia. Spanish scientists have discovered that breast milk contains selenium.

Selenium and neurological diseases

Selenoproteins are important for a variety of functions in the central nervous system. The selenium-containing GPX antioxidants counteract oxidative stress. This is highly important for the brain because it is more vulnerable to oxidative stress due to the large blood supply combined with its high content of iron and unsaturated fatty acids.
Selenium deficiency may cause a lack of certain neurotransmitters and an increased risk of neurological disorders. In patients with Alzheimer’s disease, it has been observed that selenium concentrations were around 60 percent lower than in healthy controls. A team of scientists from Munich in Germany has mapped out the more specific mechanisms and demonstrated how certain selenium-containing antioxidants (GPX4) protect brain neurons against ferroptosis, a type of cell death caused by iron accumulation and lipid peroxidation.

Selenium elongates the telomeres – the cellular aglets

Cells are constantly being replaced. Still, there is a natural limit to how many times a cell can replicate. It all depends on the telomeres that are located at the end of the chromosome ends. Just like aglets prevent shoelaces from fraying, telomeres protect the chromosome ends. Once the telomeres have become too short, however, the cells stop dividing. Instead, they self-destruct in a natural process called apoptosis.
Stress, lack of sleep, inflammation, and chronic diseases all contribute to the shortening of telomeres and, consequently, the lifespan of humans and their cells. Chinese researchers have found a direct link between total selenium intake and telomere length.

Selenium levels in the blood and mortality

Margaret Rayman, a British professor, has conducted a study that shows a relation between levels of selenium in the blood and mortality.

Levels of selenium in blood (serum):

• Below 105 micrograms per liter = increased mortality
• 105-107 micrograms per liter = mortality below average
• 130-150 micrograms per liter = lowest mortality

The average serum selenium level in Europe is between 80-100 micrograms per liter, a level that increases the risk of early death.

Mercury disrupts selenium’s functions

We all get exposed to mercury from the air, water supply, predatory fish, amalgam fillings, etc. Mercury accumulates in the body and can cause neurological damage, fetal damage, impaired immunity and other problems. Mercury binds chemically to selenium and forms a harmless and inert compound called mercury selenide. The problem with this chemical “bromance” is that is steals selenium that is otherwise needed to form the vital selenoproteins. The more mercury you get exposed to, the more selenium you will need to consume to outweigh the difference. As long as there is plenty of selenium in the body to compensate for any shortcoming, there is no immediate threat.
Mercury accumulates massively on its upward journey through the food chain. Therefore, it is a good idea to consume fish from pure waters and preferably fish from the lower parts of the food chain – such as herring, anchovies, mackerel, and salmon. These fish have a more favorable mercury-selenium ratio and are therefore safer to eat.

Official and optimal selenium recommendations

In Denmark, people are advised to get at least 55 micrograms of selenium daily. Around 20 percent of the population gets less than that. Studies show that it takes at least 100 micrograms of selenium daily to properly saturate selenoprotein P, a selenoprotein that is used as a marker of the body’s selenium status. In Finland, where selenium is added to agricultural fertilizers, people get around 100 micrograms daily. Multiple studies of thyroid disorders and cancer show favorable results with 200 micrograms daily as supplementation.
A daily safe upper intake level of 300 micrograms has been established by the European Food Safety Authority (EFSA). Selenoproteins work in synergy with nutrients like vitamin E, so it is essential in any case to try to eat a diet that is as balanced as possible.

Important selenium compounds and their function

• Deiodinase type 1-3: Thyroid hormones
• GPX 1-6 (Glutathione Peroxidase): Powerful antioxidants
• Selenoptotein S: Regulation of cytokines and inflammatory response in cells
• Selenoprotein P: Antioxidant and selenium transport in the body
• Selenoprotein R and N1: Antioxidants with many other functions
• Selenoprotein M: Large quantities in the brain. Its function remains unclear.
• Selenoprotein T: Involved in cellular structure and protein structure
• TXNRD 1-3: Antioxidants, mitochondria, energy turnover, metabolism
• MSRB1: Repair of oxidative damage
• Methyl selenol: Counteracts uncontrolled production of problematic NKG2D ligands and their presence in the blood

Even minor selenium deficiency causes selenoproteins not to function properly

References

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Selenmangel.dk. Selen, kviksølv og fiskespisning