Selenium in the Diet: How Soil Shapes Nutritional Health

Plant foods are the main dietary sources of selenium worldwide, but their selenium content depends largely on the soil in which they are grown. Selenium is a trace mineral that plants absorb through their roots, and its concentration in crops varies dramatically from one region to another. As a result, local soil conditions play a major role in determining the selenium intake of nearby populations.

In the United States, soils in the high plains of northern Nebraska and the Dakotas are particularly rich in selenium. People living in these regions typically have higher dietary selenium levels than those in other parts of the country. Conversely, in some parts of China and Russia, soils are severely depleted of selenium. Populations in these areas often experience dietary deficiencies that can lead to serious health problems, such as Keshan disease—a potentially fatal heart condition first identified in selenium-poor regions of China.

While plants are the foundational source of selenium in the food chain, animal products also contribute significantly. Livestock that consume grains or forages grown in selenium-rich soils tend to accumulate higher levels of the mineral in their tissues. Consequently, meats, eggs, and seafood can be valuable dietary sources of selenium. In the United States, meats and bread provide much of the population’s selenium intake, reflecting the country’s selenium-rich agricultural soils and fortification practices.

Among plant-based foods, nuts—especially Brazil nuts—stand out as exceptionally rich sources. A single Brazil nut can supply more than the daily recommended intake of selenium. Walnuts and other nuts also contain meaningful amounts, making them beneficial additions to a balanced diet. Recent studies emphasize the role of selenium in supporting immune function, thyroid health, and antioxidant defense, underscoring the importance of maintaining adequate intake through diverse, nutrient-rich foods.
Selenium in the Diet: How Soil Shapes Nutritional Health

Selenium: An Essential Nutrient for Health and Immunity

Selenium is a vital trace mineral that plays a crucial role in numerous bodily functions, including antioxidant defense, thyroid hormone metabolism, and immune system support. As an essential micronutrient, the body cannot produce selenium, making dietary intake necessary for maintaining optimal health. Deficiencies can lead to weakened immunity, cognitive decline, and an increased risk of chronic diseases, while excessive intake may cause toxicity.

A well-balanced diet with selenium-rich foods ensures sufficient intake. Brazil nuts are the most concentrated dietary source, with just one or two nuts providing more than the recommended daily intake. However, due to their exceptionally high selenium content, overconsumption should be avoided to prevent toxicity.

Seafood is another excellent source, particularly fish such as tuna, sardines, halibut, and salmon. These not only supply selenium but also offer omega-3 fatty acids, which contribute to cardiovascular and brain health. Shellfish like shrimp and oysters are also selenium-rich, making them valuable dietary additions.

Meat and poultry provide significant amounts of selenium, with chicken, turkey, and beef being notable sources. Organ meats, such as liver and kidney, contain even higher levels. Dairy products, including milk and eggs, offer moderate amounts, making them good options for those who consume animal-based foods.

For individuals following a plant-based diet, whole grains such as brown rice, barley, and whole wheat are beneficial sources. Selenium content in grains varies depending on soil quality, with some regions producing crops with lower selenium levels. Vegetables such as spinach, mushrooms, and broccoli contribute modest amounts, and legumes like lentils and beans provide additional sources for vegetarians.

Recent research suggests that selenium’s antioxidant properties may help reduce inflammation and oxidative stress, potentially lowering the risk of cardiovascular diseases, neurodegenerative disorders, and certain cancers. It also plays a role in reproductive health, with studies linking adequate selenium levels to improved fertility in both men and women. Additionally, selenium supports the immune response, aiding in protection against infections and viruses, including potential benefits in combating respiratory illnesses.

Ensuring a well-rounded intake of selenium-rich foods can help maintain overall health and prevent deficiencies. By incorporating a variety of these foods into daily meals, individuals can support essential bodily functions and long-term well-being.
Selenium: An Essential Nutrient for Health and Immunity

Selenium: A Key Nutrient for Immune Health and Antioxidant Support

Selenium, an essential trace element, plays a pivotal role in supporting immune health by stimulating the development and function of all types of white blood cells. These cells, including lymphocytes and natural killer (NK) cells, are critical in the body's defense system, protecting against invaders such as bacteria, viruses, and other pathogens. Selenium enhances their ability to activate and effectively respond to threats, making it particularly valuable in combating infections like the flu.

Lymphocytes, responsible for adaptive immunity, rely on selenium for optimal functioning. NK cells, part of the innate immune system, are directly involved in detecting and destroying infected or abnormal cells. Selenium's influence on these cells underscores its role in enhancing both immediate and long-term immune responses. Research has shown that selenium deficiency can lead to impaired immunity, increasing susceptibility to infections and prolonging recovery periods.

Selenium also works synergistically with vitamins E, A, and C as a powerful antioxidant. Together, these nutrients neutralize harmful free radicals that can damage cells and weaken the immune system. This antioxidant activity reduces inflammation, a factor in many chronic diseases, and supports cellular repair and regeneration. Vitamin E enhances selenium’s antioxidant potential, while vitamins A and C contribute to the maintenance of epithelial barriers and immune cell function, further boosting the body's defense mechanisms.

Recent studies highlight selenium's broader implications in global health. Regions with selenium-deficient soils often report higher incidences of infectious diseases and compromised immune resilience. During the COVID-19 pandemic, for instance, some research suggested that adequate selenium levels might influence outcomes by mitigating oxidative stress and enhancing immune response.

Dietary sources of selenium include Brazil nuts, seafood, meat, and eggs, offering a natural way to maintain optimal levels. However, excessive intake can be harmful, emphasizing the importance of balanced supplementation when dietary sources are insufficient.

In conclusion, selenium is a vital nutrient for immune function, supporting white blood cell activity and collaborating with key vitamins to protect against oxidative damage. Ensuring adequate selenium intake is essential for maintaining a robust immune system and overall health.
Selenium: A Key Nutrient for Immune Health and Antioxidant Support

Smoking can deplete selenium

Smoking is a widely accepted practice in Bangladeshi men and is associated with socializing, sharing, and male identity. Study in Bangladesh published in Nutrition Journal (Nutr J. 2004; 3: 18) shows that smoking has been associated with lower selenium levels in the body.

Selenium counteracts many of the toxic effects of smoking tobacco. Smoking depletes the body's selenium supplies. In the liver this mineral retard the conversion of hydrocarbons into carcinogens — an important function in human polluted environment.

According to research published in Toxicological Sciences (Toxicol Sci. 2009 Oct; 111(2): 247–253), cigarette smoke increased cell proliferation in the terminal bronchioles and large airways, but not in alveoli. High-selenium diets inhibited cell proliferation in the alveoli, terminal bronchioles and large airways areas in both control and smoke-exposed mice. Increasing the dietary selenium level led to increased selenium levels in the blood and lung.
Smoking can deplete selenium

Selenium: Immune Supportive Mineral

Dietary Se is vital in trace amounts and is attained through a wide variety of food sources including grains, vegetables, seafood, meats, dairy products, and nuts.

Selenium is a potent nutritional antioxidant that carries out biological effects through its incorporation into selenoproteins and selenoproteins are involved in the activation, proliferation, and differentiation of cells that drive innate and adaptive immune responses.

Selenium and selenoproteins are also involved in immunoregulation, which is crucial for preventing excessive responses that may lead to autoimmunity or chronic inflammation.

Many members of the selenoprotein family (among 25 selenoprotein which have been identified) function as enzymes involved in redox reactions and the most completely characterized selenoprotein enzymes associated to immune system include glutathione peroxidases, thioredoxin reductases, iodothyronine deiodinases, methionine-R-sulfoxide reductase B1, and selenophosphate synthetase 2.

As an immune supportive mineral, selenium also stimulates the development and function of all types of white blood cells and increases the ability of lymphocytes and NK cells, or killer cells, to activate and respond to aggressors such as bacteria and viruses, including the flu. Selenium functions synergistically with Vitamin E, A and C as an antioxidant.

Selenium deficiency has long been documented to negatively impact immune cells during activation, differentiation, and proliferation. This is associated to increased oxidative stress.
Selenium: Immune Supportive Mineral

Selenium and prevention of cancer

Selenium is nutritionally essential for humans but is toxic at higher levels, with a narrow safe range of intake. Selenium-containing compounds are known to play an important role in protection against several diseases, including cancer.

From the late 1960s, a few observational studies reported that people with high levels of selenium in their diet or in their body tissues had lower risk of cancer, and some laboratory studies showed that selenium could inhibit the growth of cancer cells. This led to widespread interest in selenium supplements.

It was observed that people with higher levels or intake of selenium had lower frequencies of certain types of cancers such as lung, bladder and prostate cancer, but no difference for other types such as breast cancer.

Newly-published prospective studies on oesophageal, gastric-cardia and lung cancer have reinforced previous evidence, which is particularly strong for prostate cancer. Interventions with Se have shown benefit in reducing the risk of cancer incidence and mortality in all cancers combined, and specifically in liver, prostate, colo-rectal and lung cancers. The effect seems to be strongest in those individuals with the lowest Se status.

The World Cancer Research Fund found in 2007 that there was probable evidence that selenium and selenium supplements reduced the risk of prostate cancer, and limited suggestive evidence that they reduced the risk of lung and bowel. Selenium was also linked to a limited suggestive lower risk of stomach cancer, and selenium supplements to a limited suggestive increased risk of skin cancer.
Selenium and prevention of cancer

Biological functions of selenium

The element that was previously considered to be toxic turned out to be present in the human body in amounts of 10–15 mg, and almost every cell of human body contains it. Very small quantities of selenium are required to maintain proper health in both animals and humans and this selenium must be obtained through dietary sources.

The necessity for selenium is most likely related to its presence in particular proteins termed selenoproteins. There are around 25 selenoproteins in humans and many of these are enzymes that act to protect the body against oxidative damage.

Selenium contributes to growth, supports healthy muscle activity, reproductive organs, reduces the toxicity of certain elements such as mercury, supports the immune system, and even delays the spread of certain viruses such influenza, Ebola, HIV.

The most important role of selenium is its antioxidant effect. This is expressed by the interaction with various enzymes. It plays a key role in the function of the glutathione peroxidase enzyme, which responds to hydrogen peroxide and other harmful lipids and phospholipid hydroxides to prevent harmful free radicals, inhibit DNA damage and the development of metabolic active carcinogens.

Supplementation with selenium, even in “selenium-replete” individuals, has been shown to have marked immunostimulant effects, including an enhancement of proliferation of activated T-cells otherwise known as clonal expansion. Lymphocytes from subjects supplemented with selenium (as sodium selenite) at 200 mcg/day, showed an enhanced response to antigen stimulation and an increased ability to develop into cytotoxic lymphocytes and destroy tumor cells.

The antioxidant effect of selenium can prevent the oxidation of LDL cholesterol, reduce inflammation, strengthen the immune system, help protect the body against oxidative stress, and thereby indirectly reduce HIV virulence.

The pathway for synthesis of the thyroid hormones tetra-iodothyronine (T4) and 3,30 ,50 tri-iodothyronine (T3) highlighting the roles of selenoproteins. The redox protective effects of selenoproteins may be of particular importance in the thyroid gland, whose long-lived cells generate H2O2 (and so also reactive oxygen species [ROS]) required for the synthesis of thyroid hormones.

Selenium has long been recognised in animal husbandry as being essential for successful reproduction.25 Idiopathic miscarriage has been shown to be associated with Se deficiency in veterinary practice26 while in sheep, administration of Se supplements has been shown to prevent early pregnancy loss.
Biological functions of selenium

The effects of selenium deficiency on human health

Selenium is a naturally occurring metalloid element, which is essential to human and other animal health in trace amounts.

Selenium deficiency produces changes in several metabolic functions, including the immune system. Selenium is an essential mineral for the efficient operation of many aspect of the immune system.

In the mouse and squirrel monkey, selenium deficiency is associated with loss of hair, emaciation, and severe lesions in liver and muscles. Both chronic and acute forms of myopathy have been reported in horses. 

Selenium deficiency has been associated with HIV disease progression and mortality. In Africa, lower levels of selenium in pregnant women has been found to be predictive of higher risk of intrapartum transmission and fetal and child death.

Recent research has shown that selenium deficiency has adversely affects thyroid hormone metabolism, which is detrimental to growth and development.

In 1979, Chinese scientists first described the relations ship of selenium to Keshan disease. Keshan disease is related to a low dietary selenium intake and low blood and hair selenium levels.

Selenium deficiency has also implicated in the incidence of bone and joint condition (Kashin-Beck disease) in humans in various part of China. Necrotic degeneration of the chondrocytes is the most storing pathologic feature of this disease.
The effects of selenium deficiency on human health

Selenium Deficiency

Selenium Deficiency
Selenium deficiency is most commonly seen in parts of China where the selenium content in the soil, and therefore selenium intake, is very low. Selenium deficiency is linked to Keshan Disease.

The most common signs of selenium deficiency seen in Keshan Disease are an enlarged heart and poor heart function.

Since the etiology of the disease was unknown, it was given the name Keshan disease after the place her where it was first discovered.

Keshan disease has been observed in low-selenium areas of China, where dietary intake is less than 19 mcg per day for men and less than 13 mcg per day for women.

This intake is significantly lower than the current RDA for selenium. Selenium deficiency also may affect thyroid function because selenium is essential for the synthesis of active thyroid hormone.

Researchers also believe selenium deficiency may worsen the effects of iodine deficiency on thyroid function, and that adequate selenium nutritional status may help protect against some of the neurological effects of iodine deficiency.

Selenium deficiency has been seen in people who rely on total parenteral nutrition (TPN) as their sole source of nutrition.

TPN is a method of feeding nutrients through an intravenous (IV) line to people whose digestive systems do not function.

Forms of nutrients that do not require digestion are dissolved in liquid and infused through the IV line. It is important for TPN solutions to provide selenium in order to prevent a deficiency.

Physicians can monitor the selenium status of individuals receiving TPN to make sure they are receiving adequate amounts.

Severe gastrointestinal disorders may decrease the absorption of selenium, resulting in selenium depletion or deficiency.

Gastrointestinal problems that impair selenium absorption usually affect absorption of other nutrients as well, and require routine monitoring of nutritional status so that physicians can recommend appropriate treatment.

Selenium deficiency and other other disease
Selenium deficiency ,may also be related to several other health condition. A low selenium status has been linked with an increased risk of pre-eclampsia and spontaneous abortions.

A number of studies have found evidence that an adequate supply of selenium is essential for male fertility.

Selenium deficiency has also been linked to the occurrence and severity of viral infection. It has been shown, under experimental conditions, that severe selenium deficiency in vitamin E-deficient hosts can change the mutation rates of RNA viruses, such as influenza, measles hepatitis and HIV, and thus increase their virulence.

It has shown that a mild strain of influenza virus exhibit increased virulence when given to selenium deficient mice and that this is accompanied by multiple changes in the viral genome in a segment previously thought to be relatively stable.

Selenium: The Immune System Mineral

Selenium is an essential trace mineral that can make a life-or-death difference and that many of us lack. Selenium is an antioxidant key to preventing cancer and stopping the progression of HIV infection from developing into AIDS.

Research suggests that selenium can protect humans against cancer of the lung, ovaries, breast, colon, liver, cervix, skin, stomach and uterus. When sufficient selenium levels are achieved, the risk of getting cancer is half that of a person who is selenium deficient. There are few good food sources of selenium, so supplementation may be the best way to obtain selenium's protective benefits.

As an immune supportive mineral, selenium stimulates the development and function of all types of white blood cells and enhances the ability of lymphocytes and NK cells, or killer cells, to activate and respond to invaders such as bacteria and viruses, including the flu. Selenium works synergistically with Vitamin E, A and C as an antioxidant.

In addition, Selenium binds with many toxic minerals such as arsenic, cadmium, lead, and mercury and facilitates their excretion from the body. By detoxifying per oxidized fats, via its role in the enzyme glutathione and peroxidase, selenium inhibits their carcinogenicity (cancer promoting traits). Selenium also counteracts many of the toxic effects of smoking tobacco.

Smoking depletes the body's selenium supplies. In the liver this mineral retards the conversion of hydrocarbons into carcinogens — an important function in our polluted environment. Good food sources include Brasis nuts, brewer's yeast, organically grown vegetables, sesame seeds, garlic, seafood, liver, and mushrooms. However, modern methods of farming and processing foods has depleted their nutritional value of this much needed mineral, along with other essential minerals.

Selenium Supplementation May Reduce Cancer Risk
One in every four deaths in this country is caused by cancer. That's 1,500 people each day. Many of these cancers are caused by our own bad behaviors - tobacco and alcohol use, lack of exercise, and poor diet - which has led researchers to investigate the ability of nutritional supplements to reduce cancer risk.

There's now convincing evidence that selenium(an essential mineral found in various foods such as Brazil nuts and mushrooms) when taken daily as a supplement can significantly reduce the risk of cancer.

In one clinical study, the risk of prostate cancer was reduced 63% in men supplementing with selenium compared to a placebo group. This result has created tremendous interest in the medical community and the National Cancer Institute has funded a much larger study called SELECT (Selenium and Vitamin E Cancer Prevention Trial) that will enroll 32,000 male subjects to better determine selenium's ability to prevent cancer.

Selenium: The Immune System Mineral