Selenium

Why selenium is good for you

• Selenium is important for thyroid gland health
  It helps the thyroid gland work properly and reduces goitre (where the thyroid gland increases in size and stops working as effectively). Selenium is also required to prevent hypothyroidism, which affects not just the thyroid gland, but the whole body, which slows down due to they thyroid gland’s impact on metabolism in the body on a general level
• Selenium works even better with the other antioxidants
  The antioxidant action of selenium is fortified when it is in the company of other antioxidants – vitamin E and perhaps also vitamin A. Several studies have shown the synergistic effect of these antioxidants when they are combined – selenium when combined with vitamin E has more potent antioxidant effects than just either alone (although both are really potent antioxidants, they are even more powerful when they are used together). The studies have shown that people who have died of cancer have been found to have lower blood levels of selenium, vitamin E and vitamin A, when compared to healthy (cancer-free) people.
• Selenium has anti-ageing properties
  Selenium’s role as an antioxidant, fighting and neutralising the effects of free radicals protects the body cells from oxidative damage, including ageing of the cells. It also removes toxic minerals such as mercury, lead and cadmium from the body

Selenium is of one the two most important minerals for the thyroid gland, to ensure it is healthy and functioning properly

Important selenium facts

• The thyroid gland contains the highest levels of selenium of any other tissue in the whole body
• Selenium helps with alleviating menopausal symptoms in women
• It helps men to produce healthy sperm
• Tissue elasticity and pancreatic function is also dependent on this mineral
• It is helpful in fighting infections since it stimulates increased antibody response to infections and promotes more energy in the body
• Selenium is a potent antioxidant
• People living in areas where the soil is poor in selenium, should pay attention to their selenium intake
• Selenium supplements should contain methionine as it detoxifies excess amounts of selenium
• Sodium selenate is also less toxic than sodium selenite
• Selenium is very important for the health of the thyroid gland and the heart
• The safest supplementation form of selenium is selenomethionine, which has a selenium molecule attached to a methionine molecule to create this compound. The methionine helps to detoxify any excess selenium (as selenium can cause toxic symptoms when it is taken in excess) and ensures that the selenium performs its duties effectively. Sodium selenate is another supplement form, which is less toxic than sodium selenite

Selenium works best with

• Vitamin B3 (niacin)
• Vitamin C
• Vitamin E (tocopherol)
• Co Enzyme Q10
• Cysteine
• Glutathione
• Methionine
• Iodine
• Iron
• Zinc

Selenium and health

• Cancer – in studies with animals it has been shown that high (therapeutic) levels of selenium reduces cancer in animals. Geographic studies have shown that people who live in areas with low soil selenium and also have relatively low selenium intakes have higher cancer mortality rates. In one trial undertaken in an area of China, higher selenium intake showed a 35% reduction in cancers. Other studies, in other areas have confirmed this result
• The heart
  Selenium’s antioxidant properties are helpful in making the blood less “sticky”, which is helpful in preventing heart attacks and strokes. Another study in Finland showed that people with low selenium blood levels were significantly more likely to die from heart disease. Other research has shown people with significant selenium deficiency – for example people receiving long term intravenous feeding and alcoholics with cirrhosis of the liver – suffer from heart problems that respond positively to selenium supplementation. Several studies have shown that selenium has a protective effect against the development of heart attack and especially dying from heart attack
• The immune system
  Selenium deficiency has been associated with impaired function of the immune system. Good selenium levels stimulate the immune system into action to protect the body from viral or bacterial (or other pathogen) infection. Selenium’s role as a potent antioxidant helps the immune system fight and neutralise free radicals in the body
• Viruses
  Some researchers have shown that in selenium-deficient animals a harmless virus can mutate into a virulent form capable of causing more severe ill health and death. This has also been followed up and confirmed by other studies
• Selenium’s potent antioxidant properties
  Selenium is a potent antioxidant which stops the potentially damaging effects that can be caused by free radicals. Selenium does this by activating the antioxidant amino acid glutathione through to the enzyme glutathione peroxidase, which is the substance that helps protect the body cells from the damaging oxidisation effects of free radicals. Studies have shown when selenium has been supplemented it provides a protective antioxidant effect on the body, lessening the effects of many conditions that proliferate under oxidative stress, such as cancer, heart disease and viral illnesses. Other research shows that selenium helps to repair cells in the lungs, heart, thyroid and other tissues damaged by oxidative stress. Selenium’s antioxidant actions may help prevent the the two most common causes of impaired vision and blindness in older people, cataracts and macular degeneration, by fighting and neutralising free radicals that attribute to these conditions
• Selenium detoxifies the body of heavy metals
  Many studies have shown that selenium helps to detoxify the body from heavy metals such as mercury and arsenic by protecting the body against the toxic effects of these heavy metals and enabling the liver to detoxify them safely and eliminate them from the body through the urine
• Selenium promotes normal growth and development
  Selenium is combined with proteins to make selenoproteins, which are important antioxidant enzymes. One of these selenoproteins, Thioredoxin reductase also recycles lipoic acid and vitamin C, regulates the metabolism of vitamin K3 and acts to regulate normal cell growth, maintenance and development. Selenium also assists in the synthesis of protein for use in the growth and development of body tissues
• Selenium has beneficial effects on diabetes
  Research shows that selenium not only restores normal glycaemic control but it also prevents or alleviates the adverse effects that diabetes has on cardiac, renal and platelet (clotting) function. This is a result of selenium’s effect on an enzyme that is involved in insulin signalling to the cells
• Selenium may be linked to sperm quality and male fertility
  Research links low selenium levels to decreased sperm quality, which impacts male fertility adversely. The research shows that the link between low selenium, sperm quality and male fertility is GPX4, an enzyme which is essential to allow the production of the correct architecture of the mid portion of sperm, that which allows it to “swim” properly
• Selenium has anti-inflammatory properties
  Studies show that selenium has potent anti-inflammatory properties. Inflammation causes a hormonal chemical called prostaglandin to be released. Selenium inhibit s the release of prostaglandin, which is why it could be useful for people with arthritis and other autoimmune diseases. Selenium’s antioxidant and anti-inflammatory actions may be enhanced when combined with vitamin E

Future research

• HIV/AIDS – there is evidence that selenium levels decrease as the disease progresses, even before malnutrition is presented. Several studies are underway and show some improvement in symptoms of people with HIV/AIDS with selenium supplement but do not decrease mortality or disease progression. More research is underway

People who wish to take an selenium supplement should talk to a medical professional before taking it.

Selenium deficiency

According to a number of researchers, selenium deficiency could be more prevalent than previously thought, due to the depletion of selenium in soil (which is how foods rich in selenium obtain it). Some scientists believe that increasing selenium may be necessary to help combat a number of illness that a deficiency of selenium is associated with (cancer, cardiovascular disease). Reviews are currently underway to determine if selenium fortification is required, but results of these reviews are not yet completed.

Groups at risk of selenium deficiency

• Men – men need more selenium than women as it is lost in the seminal fluid
• Men of reproductive age – studies who that low selenium intake is associated with low sperm quality and thus with male fertility
• Chronically ill patients – muscular weakness, muscle wasting, and cardiomyopathy (inflammation and damage to the heart muscle) have been noted in these patients. They may be deficient in selenium, because their illness could be depleting the body of this very potent anti-cancer, anti-viral antioxidant and may need supplementation
• People with large sections of their small intestine removed – these people have impaired absorption of selenium and may need supplementation
• People with severe gastrointestinal problems, such as Crohn’s disease – these people have impaired absorption of selenium and may need supplementation
• People on specialised medical diets to treat metabolic disorders – people on these diets (ie one for as phenylketonuria – PKU), are often low in selenium due to the restrictions of their diet and may need supplementation
• People on a severely calorie reduced diet – severe calorie restricted diets may not provide enough selenium-rich foods to reach their daily intake of selenium. This may cause deficiency not just in selenium, but also in many other nutrients.
• People living in areas with selenium-depleted soil – could become deficient in selenium because the food they eat does not have enough selenium to reach their recommended daily intake. Severely selenium depleted soil may cause really severe selenium-deficiency disorders.

People in these groups at risk of deficiency should talk to a medical professional about selenium supplements before taking them.

Symptoms of selenium deficiency

Selenium deficiency occurs when there is less than 40mcg intake of selenium per day. Selenium deficiency is associated with problems with the thyroid gland. Some researchers believe that around 40% of the population is at risk of selenium deficiency.

Symptoms of selenium deficiency

• Thyroid disorder (hypothyroidism)
• Cardiomyopathy
• Cognition problems with learning, remembering
• Depressed mood
• Frequent infections
• Heart disease
• High cholesterol levels
• Liver damage
• Muscle pain and degeneration
• Premature ageing
• Sterility (in males)

People who experience any of the symptoms above should seek the advice of their doctor about selenium supplementation.

Diseases caused by severe selenium deficiency

There are two main diseases that can occur with extreme selenium deficiency and both are very serious health conditions.

Keshan’s disease

This is a disease which affects the heart and it occurs mainly in selenium-deficient soils in certain regions of China. The acute form of Keshan’s disease is characterised by the sudden onset of cardiac insufficiency, while the chronic form results in moderate to severe heart enlargement with varying degrees of cardiac insufficiency. The incidence of Keshan disease is closely associated with very low dietary intakes of selenium and poor selenium nutritional status. Selenium supplementation has been found to protect people from developing Keshan disease but cannot reverse heart muscle damage once it occurs.

Kashin-Beck disease

Kashin-Beck disease is characterised by the degeneration of the articular cartilage between joints (osteoarthritis) and is associated with poor selenium status in areas of northern China, North Korea, and eastern Siberia. The disease affects children between the ages 5 and 13 years. Severe forms of the disease may result in joint deformities and dwarfism, due to degeneration of cartilage forming cells. Unlike Keshan disease, there is little evidence that improving selenium nutritional status prevents Kashin-Beck disease.

Selenium in food

Selenium recommended daily intake (RDI)

The tolerable upper limits should only be taken for short periods and only under medical supervision.

Toxic levels of selenium

Selenium is toxic at doses greater than 2000mcg (or 2mg).

Overdosage and toxicity symptoms – acute

Acute toxicity of selenium occurs when far too much selenium from supplements are taken – over 2mg (or 2,000mcg).

• Arthritis
• Birth defects
• Dermatitis
• Dizziness
• Fatigue
• Garlic-smelling breath or body odour
• Hair loss
• Irritability
• Irritated eyes
• Metallic taste in mouth
• Nausea and general upset stomach
• Weakness
• Yellow skin

Women who are pregnant or breastfeeding should not take silica supplements due to the unknown effect on the unborn foetus and young infant

Overdosage and toxicity symptoms – chronic

Chronic toxicity of selenium from taking higher than the therapeutic dose of selenium supplements (more than 400mcg) for a long time can cause the following symptoms:

• Brittle fingernails
• Diarrhoea
• Fatigue
• Garlic odour breath
• Irritated eyes
• Metallic taste in the mouth
• Mottled teeth
• Skin dermatitis
• Tingling sensation in hands and feet
• Weakness
• Yellow skin

People experiencing any of the above toxicity symptoms should discontinue their selenium supplements and seek medical advice. Overdosage and toxicity is more likely to occur from taking too many supplements, whereas dietary intake of selenium is highly unlikely to cause overdosage.

Precautions

Selenium, especially in the form Selenomethionine is generally safe to take and there are no cautions with any groups of people. This is because the methionine in the selenomethionine detoxifies any of the potential toxicity of the selenium and makes it much safer to take than just plain selenium with another substance.

Medications and supplements

The following are the medications and supplements that are more likely to cause a reaction with selenium supplements:

• Chemotherapy medications (Cisplatin, Doxorubicin, Bleomycin)
  Selenium may inhibit the anti-cancer effects of the chemotherapy medication Bleomycin, thereby reducing its effectiveness. On the flip side, selenium may reduce the toxic side effects associated with the chemotherapy medications Cisplatin and Doxorubicin.
• Cholesterol-lowering medications (Simvastatin)
  If cholesterol-lowering medications such as Simvastatin (which lower LDL (“bad”) cholesterol and raise HDL (“good”) cholesterol) are taken together with selenium supplements, the selenium prevents the HDL (“good”) cholesterol levels from being raise, thus inhibiting some of the effectiveness of the medication. This interactions occurs with cholesterol-lowing drugs and any antioxidant supplements.
• Vitamin C and vitamin E
  Selenium enhances the antioxidant properties of both vitamin C and vitamin E, to further prevent oxidation in body tissues and damage from free radicals, so these supplements should be taken together.

Selenium has possible adverse interactions with chemotherapy medications and cholesterol-lowering medications

Other interactions with selenium

There are none reported.

Selenium’s effect on lab tests

There are none reported.

References

• USDA National Nutrient Database – provides nutrient values for foods (accessed 5 January 2005)
• Osiecki, H. The Nutrient Bible. Bio-Concepts Publishing QLD, 2002
• Whitney EN, Cataldo DB, Rolfes SR. Understanding Normal and Clinical Nutrition, 6th Edition. Wadsworth/Thomson Learning, 2002

Last updated: 5 May 2024