Selenium is one of the key micronutrient required by our body. Though required in small quantity it plays vital role in metabolism and well being of the body. Selenium is required for various enzyme activity, increase immunity and protect body from risk of cardiovascular diseases. Benefits of Selenium are discussed in further detail in remaining sections of the article.
What is recommended selenium intake?
We get most of micronutrient requirement from our food. This micronutrients is required in small amount. Our requirement for body is roughly 1 microgram/day per kg of our weight. Recommended dietary allowance (RDA) for selenium from our food and supplements is as under
- Children 1-3 yrs : 20 micrograms/day
- Children 4-8 yrs: 30 micrograms/day
- Children 9-13 yrs: 40 micrograms/day
- Adults and children 14yrs and above: 55 micrograms/day
- Pregnant women: 60 micrograms/day
- Breastfeeding women: 70 micrograms/day
What are Natural Sources of Selenium?
Selenium is one of the minerals found in earth’s crust. Plants absorb selenium from the soil. Thus amount of selenium in plant based food vary a lot depending on soil nutrient content and quality. Brazil nuts are the richest source of selenium containing over 19mcg/gram. Food grains, sea food, meat and poultry are other major natural sources of selenium to our body. Since in Selenium attached to a protein is more easier to absorb in body, selenium obtained from animal sources is more available to body. Protein rich animal food is good source of selenium. Other exceptionally selenium-rich foods include Tuna, Shrimp, Sardines, Salmon, Turkey, Cod, Chicken, Scallops, Beef, Asparagus, Mustard seeds, herring, Brown rice, wheat germ, wheatgrass, mushroom, Garlic, Sesame seeds, flax seed, oysters and other. Since soil in US is mostly rich in selenium, a daily diet of US adult provides adequate selenium requirement. A National Health and Nutrition Study suggest with average daily intake of 106 mcg of dietary selenium, average US adult has low risk of selenium deficiency disorder.
What does Selenium deficiency cause?
Selenium deficiency is not common as our foods are able to meet the daily requirement of selenium. Further deficiency of selenium does not lead to prominent symptoms.
Cases of widespread selenium deficiency had been found in parts of China, Tibet and Russia where selenium content of soil is quite less. Keshan disease or cardiomyopathy occurred in part of China which required government to promote selenium supplementation program. Intake of selenium by average adult was found to be less than 20 mcg per day in these regions.
Selenium deficiency is also associated with male infertility and Kashin beck disease. In infants, iodine deficiency can be aggravated by selenium deficiency and increase risk of cretinism. Selenium deficiency is associated with incidence of diseases caused by inflammation and oxidative stress.
Following people group are at high risk for selenium deficiency
- People living in selenium-deficient regions including some parts of Europe, China
- People with vegan diet, unless including selenium rich grains and food in diet
- People undergoing kidney dialysis as hemodialysis removes selenium from blood
- HIV infected people have low selenium levels due to malabsorption and occurrences of diarrhea
Health benefits of Selenium
Studies have been undertaken to study benefits of Selenium in treatment of various diseases from cold to cancer. While most results so far have been inconclusive, it doesn’t undermine benefits of selenium to our body. Selenium is often present in our body bound to protein in form of Selenoproteins. Nearly 25 such selenoproteins have been isolated and found to have various crucial functions in our body. Some of the Selenoprotein types and their functions are mentioned below:
- GPx – Forms part of four glutathione peroxidase enzymes found in mammals and protects body cells from oxidative stress.
- Selenoprotein P – Two third of plasma Selenium is in form of selenoprotein P. Serves transportation of selenium to various body tissues, remove free radical and helps development of functional spermatozoa
- Selenoprotein W – Present in skeletal muscle and required for muscle metabolism
- Cytosolic selenoprotein, Prostate epithelial selenoprotein, 15kDa – Found in prostate gland and antioxidant and cancer protective in nature
- Selenophosphate synthtase, SPS2 – Required for biosynthesis of other selenoprotein
- Phospholipid hydroperoxide GPx – Present in heart and liver and prevents from oxidation by lipid peroxides.
- Sperm mitochondrial capsule selenoprotein – Assist sperm motility
- Type-I iodothyronine deiodinases – Necessary for thyroid function, aids conversion of T4 to T3,
- Thioredoxin reductases – Acts as catalyst in body metabolic process, antioxidant
- DNA-bound spermatid selenoprotein, 34kDa – GPx-like activity found in stomach and in nuclei of spermatozoa, protects sperm
- 18kDa selenoprotein – Stored in kidney and other tissues for future use in case of deficiency
In general selenium is believed to offer various health beneficial properties. Most of these benefits are basically claims which are yet to be established. Yet some of them are discussed below:
Antioxidant properties of Selenium
Selenium and selenoproteins in particular protects cells from damage from oxidation. In form of GPx (glutathione peroxidase enzyme) it plays vital role in detoxification process in body. Selenoproteins also helps recycle oxidized Vitamin C, thus indirectly offers antioxidant protection.
Free radicals in body are responsible for damage of cells leading to their death or mutation. This is the prime cause of various diseases including heart disorders, aging and cancer. With its antioxidant action selenium works together with other antioxidant nutrients like Vitamin E, Zinc, Vitamin C to protect our body.
Memory loss or cognitive decline is associated with damage to brain cells. This is mainly due to oxidative stress. Selenium as an antioxidant is helpful in preventing loss of memory. However more scientific evidence is yet to come in benefits of selenium supplements in preventing age related cognitive decline.
Skin benefits of Selenium
It is an important nutrient when it comes to nutrients for skin care regime. With its antioxidant action, selenium protects skin from harmful oxidative stress of pollution, ultraviolet light and other chemicals. They act as scavangers, help maintain elasticity of the skin. It helps in preventing aging of skin and thus prevents dark spots and wrinkles. Studies suggest that along with vitamin E, selenium supplementation can be used in treatment of acne. Some researchers believe that selenium is associated with reducing risk of skin cancer. As an anti-inflammatory agent, it is also helpful in treating psoriasis, eczema and other skin disorders.
Selenium reduces inflammation
Selenium also acts as anti-inflammatory agent in our body. It reduces inflammation caused due to oxidation in body. Clinical trial shows benefits of selenium in treating inflammatory conditions like rheumatoid arthritis, gout, eczema, pancreatitis, asthma and bronchitis. Lab studies show that Selenium supplementation was found to reduce pain and joint pain in arthritis patients.
Selenium prevents cancer?
Oxidative stress leads to damage or death of body cells. Persistent damage lead to mutation of cell which may lead to development of cancer. Once antioxidant property of Selenium is established, researchers have been keen in evaluating ability of selenium in preventing and treating cancers. Initial studies have been promising, yet inconclusive. Selenium protects body cells from damage and mutation caused by oxidation. Some selenoprotein – GPx or Se-P have been found associated with reduction of risk of prostate cancer.
Selenium supports thyroid function
Thyroid gland is important part of our endocrine system which controls the metabolic activity and other hormones in our body. Selenium concentration is highest in thyroid. Along with iodine, selenium is important for synthesis of thyroid hormone. Type I iodothyronine deiodinase is enzyme is necessary for conversion of less active thyroid hormone T4 to more active T3 is a selenium bound protein. T3 hormone is responsible for controlling our metabolic rate. Further selenium also protects thyroid gland from oxidative stress of free radicals and peroxides. In a animal study, researchers were able to induce thyroid disorders in rats with low selenium diet. Selenium supplementation was also found useful in reducing thyroid inflammation and treating autoimmune thyroiditis.
Selenium to prevent Kashin-Beck disease
Kashin–Beck disease is a chronic disorder of bones whose occurrence is prevalent in selenium deficient regions including province of China, southeast Siberia and North Korea. Symptoms of the disease involve joint pain, stiffness of joints, morning stiffness, difficulty in movement of joints in body and inflammations in joints. In this disease, cartilage cells are damage, death or retarded growth. It may lead to development of osteoarthritis. Selenium and iodine deficiency are considered one of the causes of Kashin Beck disease. Selenium supplementation has been found effective in preventing this disease.
Selenium prevents Keshan Disease
Keshan disease is a congestive cardiomyopathy in newborns. It has been linked to selenium deficiency along with presence of coxsackievirus. It was first reported in Keshan county in North east China. The disease involves inflammation of heart muscles, leading to high blood pressure or even stroke. Selenium supplementation is found effective in controlling this disease in selenium deficient China.
Selenium to eliminate dandruff
In a study, selenium sulfide was found to be effective in treating dandruff. Research is limited in area of benefits of selenium for treatment of hair and scalp. Zinc and selenium are often used in commercial shampoo for treatment of dandruff and preventing hair loss. Selenium sulfide is used in body lotions to control infections of Malassezia fungus.
Selenium protects heart
Selenium in form of Selenoproteins offers protection to heart tissues from oxidative stress and has potential to reduce risk of cardiovascular diseases. Statistical studies are yet to establish a link between reduction of such risk. Some studies have come forward showing treatment of various cardiovascular diseases like ventricular tachycardia, arrhythmia and ischemia through selenium supplementation.
Selenium important for immune sytem
It is believed that selenium activates antibodies in body which are the front line of defense against various pathogens. GPx enzymes which are essentially selenium bound proteins also protect Neutrophils (white blood cells type) from free radicals produced during ingestion of invading pathogens and thus increases immunity. Neutropenia is condition of reduced WBC neutrophils. Selenium supplementation has showed ability to correct decreasing WBC. Selenoprotein 15-kDa has been identified in T cell (type of White blood cells).
Viral infections and selenium
Selenium deficiency is often linked with occurrence of viral infection. As in case of Keshan disease, Coxackie virus becomes virulent in Selenium deficient hosts and results in heart infection. In selenium deficient people, risk of viral infection progresses are more serious. It is found that retroviruses like HIV and Coxsackie B3 can potentially destroy selenium transport by incorporating Selenium into their selenoprotein for their own protection. Such stable viral mutation has also been reported with influenza virus in selenium deficient mice.
Selenium and fertility
Selenium is found in sperm mitochondria and is required for maturation of sperm. It ensures mobility in sperm and thus fertility. Studies have found that testosterone synthesis and development of spermatozoa has been affected in selenium deficient mice. Selenium supplementation has shown increased sperm mobility in subfertile men. However high doses of selenium supplements may lead to decrease in sperm mobility.
Mood and selenium
While selenium is essential for protection of brain cells, a study showed that selenium supplementation significantly decreased anxiety, depression and fatigue. The effect was greatest in selenium deficient groups.
Selenium is available in multivitamin and multimineral supplement. Selenomethionine or of selenium-enriched yeast or sodium selenite or sodium selenate are popularly used as standalone selenium supplements. Selenomethionine is found to be easier to absorb in body as compared to other.
What are the risks of taking selenium?
400 micrograms per day is considered to be safe upper limit of selenium for adult, beyond which it is considered as overdose. Taken in normal limits it doesn’t offer any side effects. Excess intake of selenium may lead to nausea, liver or kidney problem, fever. It interacts with other medicines antacids, birth control pills, corticosteroids and others. Selenium supplements have been associated with risk of skin cancer and development of type 2 diabetes.Image Credits: Flickr - CIFOR, ARS - USDA