Selenium 200 mcg tablets are promoted to help fight cell-damaging free radicals, support healthy cholesterol levels and support thyroid hormone function.
Oral selenium supplements come in several different forms including L-selenomethionine, Se-Methyl L-Selenocysteine, sodium selenite, selenized yeast and more.
In the human body, selenium plays important roles in converting thyroid hormone into its active form, repairing DNA and helping cells to resist damage from oxidizing agents like Reactive Oxygen Species (ROS).
Selenium is also required to fight off bacterial, viral and parasitic infections and is involved in immune system function. If you don’t have enough of this mineral in your diet, you may be at risk of cardiovascular problems, poor energy levels, cognitive dysfunction, muscle weakness and higher rates of cancer.
The typical person gets enough selenium from food sources to avoid deficiency. However, there may be instances in which using an oral capsule containing this mineral may have additive benefits for human health.
Before deciding whether to buy selenium tablets online, it is important to understand how they work, the different types of products that are available, how to use and potential safety risks.



- Cofactor for antioxidant enzymes
- Supports thyroid function & metabolism
- Promotes immune function & fertility
Selenium Tablet Uses
Selenium (Se) is a trace chemical element with atomic number 34. This mineral is required by the human body in order to function normally.
It is an essential nutrient in humans, meaning it must be gained from the diet and cannot be made internally. Not getting enough puts individuals at risk of symptoms of deficiency.
We can increase our consumption of selenium by eating foods like Brazil Nuts, fish, meat products, grains and certain vegetables grown in selenium-rich soil.
Dietary supplements can also be used to ensure adequate intake. These supplements often combine this micromineral with other antioxidants such as Vitamin E and beta-carotene.
Some people who have gastrointestinal disorders like Crohn’s disease may not be able to absorb selenium from food sources properly. Using oral capsules that have been formulated for higher oral bioavailability may be beneficial.
In addition to being used to prevent a selenium deficiency, ongoing clinical research is looking into the effects of supplementing with this mineral for cardiovascular disease, thyroid disease, cancer and cognitive decline with aging.
The Natural Medicines Comprehensive Database (NMCD) states various uses for selenium pills including:
- Liver, lung, esophageal, prostate and other cancer;
- Atherosclerosis and cardiovascular disease;
- Benign prostatic hyperplasia (BPH);
- Type 2 diabetes mellitus;
- HIV/AIDS;
- Infertility;
NMCD states that selenium is also used for gray hair, chronic fatigue syndrome (CFS) and atopic dermatitis (eczema).
There are various other uses for selenium as well, but many of these uses have not been well-researched. More studies are required to determine therapeutic efficacy.
Currently the FDA has not approved this supplement as a drug for the prevention or treatment of any medical conditions.
The NMCD reports that selenium is s Likely Effective for reversing selenium deficiency and Possibly Effective for autoimmune thyroiditis, sepsis and elevated plasma fatty acid levels (dyslipidemia).
Types of Supplements
Selenium comes in several different supplemental forms, both organic (found naturally in nature) and inorganic (synthetic forms produced in a lab).
These formulations vary in terms of their cost, recommended dosage, research history, safety profile and efficacy. Some forms are believed to be better absorbed by the body and more readily used in certain physiological processes.
There are five primary types of selenium tablets for sale online. Research shows that certain inorganic forms are easily absorbed from the gut, but quickly excreted from the body. [6]
Organic forms of this mineral that are protein-bound are not filtered out by the kidneys and remain active in the body for a longer period of time. These sources are better utilized by the body and can be converted into selenoproteins that have various biological functions.
These natural sources also tend to have good oral bioavailability and uptake from the gastrointestinal tract, with 90% of selenomethionine being absorbed by the body and 50% being retained. [6]
Below is a summary of five of the most common forms of selenium found in pill tablets and their unique properties:
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- Selenium sulfide – an inorganic form commonly used as a topical anti-infective agent and not typically used in oral supplements. It is used as an ingredient in anti-itching and dandruff shampoos and creams.
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- Sodium Selenite – This inorganic form is made synthetically. While it is absorbed from the gut, it is quickly filtered out of the blood by the kidneys and may not significant improve serum selenium status.
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- Selenium-enriched yeast – This is a natural product that is made from yeast fermentation. Typically, the yeast Saccharomyces cerevisiae will be cultivated in a medium that contains rich amounts of selenium.
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- Selenomethionine This is a naturally occurring organic amino acid that plays multiple roles in the body. This form of selenium is found in high amounts in Brazil buts, soybeans and certain cereal grains.
- Se-Methyl L-Selenocysteine – This is another naturally occurring amino acid that contains selenium. It is found in Astragalus and members of the Brassica family of plants.
Purported Health Benefits
The health benefits of selenium are not yet well defined. If you are deficient in this mineral, taking more can help to improve general well-being, mood, brain function and more.
However, the majority of people in North America who eat a healthy and well-rounded diet are not deficient in this mineral. It is unclear whether increasing your intake can further boost health.
While we have a clear understanding of many of the roles that this mineral plays in the human body, it is not well understood how supplementation with selenium influences different health goals.
Selenium is the base constituent of more than two dozen selenoproteins which are involved in a wide range of biological activities in humans.
According to the National Cancer Institute, selenoproteins and other selenocompounds “represent diverse molecular pathways and biological functions.” [1]
Some of the systems that are influenced by selenium availability include:
- Thyroid function
- Immune system
- Antioxidant enzymes like glutathione
- Detoxification of heavy metals
- Recycling antioxidant capacity of Vitamin E
- Reproductive function
- Cardiovascular system
- Blood lipid regulation
- Brain functions
Selenium Supplements for Cancer
Many people take selenium tablets for their purported anti-cancer benefits and antioxidant effects.
According to the University of Illinois, research from cell culture, animal and human studies “strongly support the protective role of selenium against various types of cancer.” [2]
However, the FDA has evaluated the evidence and says it is limited and not conclusive to demonstrating a protective effect against cancer. Further studies are needed to determine health benefits.
Population studies show a correlation between adequate selenium intake and lower occurrence of certain types of cancer. Some research suggests that selenium deficiency increases the likelihood of developing prostate cancer and colon cancer.
Some of the ways that this mineral is believed to protect against cancer include:
- Modulating lipoxygenases and inactivating nuclear transcription factor;
- Promoting the natural death (apoptosis) of cancerous cells;
- Helping the body to detoxify toxic heavy metal residues;
- Supporting the normal function of the immune system;
- Reducing damage caused by oxidative stress;
Selenium might also regulate cell cycle arrest in cancer cells, decrease the activities of androgen receptors and suppress the formation of DNA adducts. [2]
More research is needed to determine whether or not selenium can influence the risk of developing cancer or mortality rates of the disease. Not all research has found positive results and there have been studied with conflicting findings.
Selenium for Cognitive Decline
If you do not get enough of this mineral in your diet, you may be at risk of age-related decline in brain function linked to low antioxidant activity.
According to a 2015 Russian research study “Selenium is vital for the brain and seems to participate in the pathology of disorders such as Alzheimer’s disease, Parkinson’s disease, amyotrophic lateral sclerosis and epilepsy.” [3]
Being deficient in selenium can lead to thyroid dysfunction, which can indirectly lead to brain fog, poor memory, fatigue, lack of concentration and other signs of mental impairment.
Studies suggest that people with lower levels of this mineral in their blood are more likely to experience cognitive decline over a long period of time. However, other studies have shown no association between selenium levels and memory performance.
In the SU.VI.MAX study, participants were given 120 mg ascorbic acid, 30 mg vitamin E, 6 mg beta-carotene, 100 mcg selenium, and 20 mg zinc per day for 8 years. After 8 years, those taking the supplement had higher episodic memory and semantic fluency test scores.
Although data from some preliminary studies on the effects of selenium on cognitive decline seem favorable, more research is needed to determine its efficacy in humans.
Selenium for Thyroid Disease
Selenium is important for your thyroid gland to work properly. This gland produces hormones that regulate metabolism, cell growth and division in the body.
If levels of these hormones are too low, physiological processes in your cells like energy production, maintenance and repair begin to slow down. This can lead to weight gain, difficulty thinking, poor immune function, poor skin and hair quality and more problems.
Taking a 200-mcg selenium tablet once daily might help to support thyroid function in people at risk of low thyroid hormone activity (hypothyroidism). It has been administered along with levothyroxine (synthetic thyroid hormone).
Research shows that oral selenium pills may improve Autoimmune thyroiditis (Hashimoto’s disease), which is a condition wherein the thyroid gland becomes inflamed because your body mistakenly produces antibodies that attack the gland.
The combination of selenium with levothyroxine seemed to reduce “thyroid peroxidase antibodies by about 6% to 30% more than placebo in adult patients with thyroiditis after 3-12 months of treatment.” [4]
Other studies have shown that selenium may be more effective in those with advanced disease states and less effective in those with low-to-moderate disease activity.
One study suggests that doses less than 200 mcg/day might not be as effective at reducing thyroid antibodies. [5]
Side Effects & Safety Rating
Selenium supplements are rated Likely Safe by the Natural Medicines Comprehensive Database, when taken short-term in standard dosages of 200 mcg – 400 mcg per day.
NMCD states that selenium deficiency is rare. The US RDA for this essential trace mineral is 55 micrograms per day. A microgram (mcg) is 1/1000th of a milligram (mg) and 1/1,000,000th of a gram (g).
Most people get enough of this compound in their diets to avoid developing symptoms of deficiency, but certain factors can put you at greater risk of being deficient.
Some of the possible symptoms of selenium deficiency include hypothyroidism, slowed thinking, extreme fatigue, goiter, miscarriage and cretinism.
Selenium toxicity is more of a concern than deficiency and may be marked by side effects including worsened symptoms of existing iodine deficiency. It is not recommended to supplement your diet with additional selenium without also supplementing with the mineral iodine.
The UL (upper tolerable limit) of selenium per day is 400 mcg. According to WebMD, if you get more than this, it could cause nausea, vomiting, irritability and/or loss of energy. Excess consumption can also cause hair loss and changes in texture of fingernails and toenails.
You should discuss using oral selenium tablets with your doctor to determine whether they are appropriate for you and which form of supplement is best for your needs.
Selenium but may cause interactions with certain health conditions, prescription medications, herbal supplements, foods and/or laboratory tests.
- Labunskyy VM1, Hatfield DL1, Gladyshev VN1. Selenoproteins: molecular pathways and physiological roles. Physiol Rev. 2014 Jul;94(3):739-77. doi: 10.1152/physrev.00039.2013.
- Naithani R1. Organoselenium compounds in cancer chemoprevention. Mini Rev Med Chem. 2008 Jun;8(7):657-68.
- Solovyev ND1. Importance of selenium and selenoprotein for brain function: From antioxidant protection to neuronal signalling. J Inorg Biochem. 2015 Dec;153:1-12. doi: 10.1016/j.jinorgbio.2015.09.003. Epub 2015 Sep 15.
- Gärtner R1, Gasnier BC, Dietrich JW, Krebs B, Angstwurm MW. Selenium supplementation in patients with autoimmune thyroiditis decreases thyroid peroxidase antibodies concentrations. J Clin Endocrinol Metab. 2002 Apr;87(4):1687-91.
- Turker O1, Kumanlioglu K, Karapolat I, Dogan I. Selenium treatment in autoimmune thyroiditis: 9-month follow-up with variable doses. J Endocrinol. 2006 Jul;190(1):151-6.
- Fairweather-Tait, Susan J, et al. "Selenium Bioavailability: Current Knowledge and Future Research Requirements." The American Journal of Clinical Nutrition, vol. 91, no. 5, May 2010, pp. 1484–1491. Accessed 21 Sept. 2016.
Article last updated on: July 3rd, 2018 by Nootriment