Author – Phoebe Chan – BSc (Hons) Nutrition and Human Health
Selenium is a trace mineral that the body needs only in small amounts. It is an essential component of various enzymes and proteins, called selenoproteins, which help make DNA and protect against cell damage and infections. It also has antioxidant properties that help break down peroxides, which can damage tissues and DNA, leading to inflammation and other health problems (1).
What is Selenium?
Selenium is an essential mineral that is required for human health. It is naturally present in many foods, added to others, and available as a dietary supplement. Selenium is a component of 25 selenoproteins, including glutathione peroxidase (2), which plays a critical role in thyroid hormone metabolism, DNA synthesis, reproduction and protection against oxidative damage (3-5).
In foods, selenium is primarily found as selenomethionine along with selenocysteine. Although it is readily absorbed by the body, selenium cannot be produced endogenously and must be obtained through the diet (5-7).
Key Benefits of Selenium Supplements
Thyroid Health Support
The thyroid gland is responsible for producing hormones that regulate metabolism, growth and development. It contains the highest concentration of selenium per gram of tissue compared to any other organ in the body. Therefore, it has critical involvement in the synthesis, activation and metabolism of thyroid hormones.
Among the most important selenoproteins are the iodothyronine deiodinases, which are enzymes responsible for converting the inactive thyroid hormone thyroxine (T4) into its biologically active form, triiodothyronine (T3). Without sufficient selenium, this conversion process can be impaired, leading to disruptions in thyroid hormone availability and cellular metabolism (8).
Antioxidant Protection
Selenium provides antioxidant protection by acting as a cofactor in selenoproteins, such as glutathione peroxidase (GPx). These play a significant role in protecting cells against oxidative damage from reactive oxygen species (ROS) and reactive nitrogen species (RNS) (9). They work by neutralising excess free radicals and protecting cells from damage caused by oxidative stress (10).
Immune System Support
Selenium supports immunity by being incorporated into selenoproteins, which regulate oxidative stress and immune cell function. It influences both innate and adaptive immune responses by modulating the production and activity of cytokines, the signalling molecules that coordinate immune activity (11).
By maintaining redox balance, selenium helps immune cells function effectively and prevents excessive inflammation. Therefore, selenium helps to ensure the body can effectively fight off infections and illnesses (12).
Fertility and Reproductive Health
Selenium supports fertility through its role in selenoproteins such as GPx, which protect reproductive cells from oxidative stress. In males, GPx reduces reactive oxygen species, preventing damage to sperm DNA and improving sperm viability (13,14). Furthermore, selenium is involved in the structural integrity of the sperm tail, which is crucial for sperm motility. Deficiency has been associated with abnormal sperm morphology and reduced motility, contributing to infertility (15).
In females, selenium helps protect developing oocytes (eggs) from oxidative damage, which is critical for proper maturation and ovulation (17). It may also support hormonal balance and reduce inflammation, factors relevant in conditions such as polycystic ovary syndrome (PCOS) (16). Higher selenium levels have been associated with improved egg quality and higher fertilisation rates during in vitro fertilisation (IVF) (18-20).
Signs of Low Selenium
Selenium is a vital trace element used in many places in our body. A lack of this mineral can be noticeable in many ways. The most important symptoms of selenium deficiency include:
General well-being
- Fatigue
Physical complaints
- Hair and fingernails: thin, dull hair, hair loss, spots on the nails
- Skin: pale and dry
- Muscle: muscle weakness, muscle pain, chronic fatigue syndrome, joint pain
- Immune system: susceptibility to infection, tendency to allergies
- Eyes: tendency towards eye disorders
- Thyroid gland: thyroid disorders (underactive), thus weight fluctuations
Mental disorders
- Nerves and mind: memory disorders, sleep disorders, depressive moods, headaches
Gender-specific disorders
- Individual symptoms in men: fertility problems
- Individual symptoms in women: during pregnancy – poorer cognitive development of the child (21)
Types of Selenium Supplements
Selenomethionine: formed in plants when selenium substitutes for sulphur during synthesis of the amino acid methionine, and becomes incorporated into proteins in place of methionine. It is the most bioavailable form of selenium and common in high quality supplements.
Selenium Enriched Yeast: where the selenium becomes organically bound to the yeast, mostly being incorporated into the yeast proteins. Therefore, the supplement consists predominantly of selenomethionine, but also has small amounts of selenocysteine, methylselenocysteine and gamma-glutamyl Se-methylselenocysteine.
Sodium selenite/selenate: inorganic forms of selenium. Selenite is the most common form of selenium used in pet foods. Selenate is the predominate form of selenium in shellfish and vegetables (other than the allium and brassica families) grown in seleniferous soil (22).
How to Choose the Right Selenium Supplement
What to look for on the label
- Third-Party certified: USP, NSF, Interntional, or ConsumerLab seals verify potency and purity
- Form clearly stated: label should say “selenomet hionine” or “selenium yeast,” not just “selenium”
- No proprietary blends: individual doses must be disclosed
- GMP certified: confirms consistent manufacturing quality
- Dose 200 mcg per serving: matches the dose used in positive clinical trials (23).
Who Should Consider Selenium Supplements
Many people will be able to get enough selenium through their diet. However, there are certain situations where they may not be able to such as:
- People living in low selenium regions who also eat a primarily plant-based diet. This is rarely seen in the US, but populations in China, Russia, and Europe are at risk as their soil is generally low in selenium.
- People with HIV. This can lead to diarrhoea, malabsorption of nutrients and decreased appetite.
- People with kidney failure undergoing dialysis. This mechanical process of filtering the blood can remove some selenium. The dietary restrictions required with kidney failure can also decrease overall food intake, leading to a risk of selenium deficiency (1).
Conclusion
Selenium is a trace mineral that plays a vital role in human health, forming part of selenoproteins. These support DNA production and protect against cell damage and infections.
While deficiency is uncommon, it is equally important to recognise that excessive intake is harmful. Consuming high selenium foods, such as Brazil nuts, in large amounts or overusing dietary supplements can quickly lead to toxic levels. Ultimately, maintaining a balanced intake is key – ensuring you gain the benefits of selenium while avoiding unnecessary risks.
Frequently Asked Questions (FAQ’s)
What are selenium supplements used for?
Selenium supplements are used to support overall health by contributing to antioxidant defence, thyroid function, and immune system support. They help the body produce selenoproteins, which play a role in protecting cells from damage.
Who should consider taking selenium supplements?
Most people get enough selenium through a balanced diet. However, individuals with restricted diets, certain medical conditions, or low soil selenium levels in their region may benefit from supplementation – ideally under professional guidance.
Can you get enough selenium from food alone?
Yes, in most cases. Foods like Brazil nuts, seafood, meat, eggs, and whole grains are rich in selenium. Supplements are usually only necessary when dietary intake is insufficient.
References
- https://nutritionsource.hsph.harvard.edu/selenium/
- https://pubmed.ncbi.nlm.nih.gov/27645994/
- Sunde RA. Selenium. In: Ross AC, Caballero B, Cousins RJ, Tucker KL, Ziegler TR, eds. Modern Nutrition in Health and Disease. 11th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2014:225-37.
- Hong LK, Diamond AM. Selenium. In: Marriott BP, Birt DF, Stallings VA, Yates AA, eds. Present Knowledge in Nutrition. 11th ed. Cambridge, MA: Academic Press; 2020:443-56.
- Lei XG, Rayman M, Sunde RA. Selenium. In: Tucker KL, Ross CA, Jensen GL, Torger-Decker R, Duggan CP, eds. Modern Nutrition in Health and Disease. 12th ed. Burlington, MA: Jones & Bartlett Learning. In press. 2024.
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- https://pmc.ncbi.nlm.nih.gov/articles/PMC2698273/
- https://www.healthline.com/nutrition/selenium-benefits#1-Acts-as-a-powerful-antioxidant
- https://www.cambridge.org/core/journals/proceedings-of-the-nutrition-society/article/selenium-and-the-immune-response/F42969F2CFEDA53962077B33A1DA40F5
- https://www.cambridge.org/core/journals/public-health-nutrition/article/selenium-selenoproteins-and-human-health-a-review/E15A75ABD1E480DDD7F4FDE71FA1B5A6
- Qazi IH, Angel C, Yang H, Zoidis E, Pan B, Wu Z, et al. Role of Selenium and Selenoproteins in Male Reproductive Function: A Review of Past and Present Evidences. Antioxidants (Basel). 2019 Aug 2;8(8):268.
- Guerriero G, Trocchia S, Abdel-Gawad FK, Ciarcia G. Roles of reactive oxygen species in the spermatogenesis regulation. Front Endocrinol (Lausanne). 2014 Apr 22;5:56.
- Kaltsas A. Oxidative Stress and Male Infertility: The Protective Role of Antioxidants. Medicina (Kaunas). 2023 Oct 4;59(10):1769.
- Sharma P, Gupta V, Kumar K, Khetarpal P. Assessment of Serum Elements Concentration and Polycystic Ovary Syndrome (PCOS): Systematic Review and Meta-analysis. Biol Trace Elem Res. 2022 Nov;200(11):4582-4593.
- Grzeszczak K, Łanocha-Arendarczyk N, Malinowski W, Ziętek P, Kosik-Bogacka D. Oxidative Stress in Pregnancy. Biomolecules. 2023 Dec 9;13(12):1768.
- Sabatini L, Wilson C, Lower A, Al-Shawaf T, Grudzinskas JG. Superoxide dismutase activity in human follicular fluid after controlled ovarian hyperstimulation in women undergoing in vitro fertilization. Fertil Steril. 1999 Dec;72(6):1027-34.
- Paszkowski T, Traub AI, Robinson SY, McMaster D. Selenium dependent glutathione peroxidase activity in human follicular fluid. Clin Chim Acta. 1995 May 15;236(2):173-80.
- Dahlen CR, Reynolds LP, Caton JS. Selenium supplementation and pregnancy outcomes. Front Nutr. 2022 Oct 31;9:1011850.
- https://biogena.com/en-gb/knowledge/guide/selenium-deficiency_bba_5287138
- https://www.zrtlab.com/blog/archive/selenium-supplementation-in-the-diet/
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