Selenium: An Essential Trace Mineral for Metabolic Balance and Body Protection

Selenium (Se) is an essential trace element that, despite being needed only in very small amounts, plays a major role in maintaining vital functions. Selenium is not merely a passive participant in the body: it is a key component of selenoproteins—specialised proteins that act as enzymes in crucial biochemical processes, from protecting cells against oxidative stress to regulating thyroid function.

A primary role in the body – antioxidant defence

Selenium’s central role is most clearly seen through its presence in the enzyme glutathione peroxidase. This enzyme is part of the body’s primary defence system, neutralising free radicals. Without adequate selenium, cells become more susceptible to “oxidative damage,” which accelerates ageing and the development of chronic inflammation.

Selenium also plays an important role in immune function. It contributes to cytokine regulation—cell-signalling molecules that guide immune responses. Research indicates that selenium is required for the development of acquired immunity and supports defence against pathogenic infections. Selenium deficiency has been associated with impaired immune function.

Focus on digestion and gut health

Although selenium is often discussed in the context of immunity, its role in the digestive system is also important:

• Integrity of the intestinal barrier: selenoproteins help maintain tight junctions between intestinal epithelial cells. Low selenium status has been linked to increased intestinal permeability (“leaky gut”) and inflammatory bowel diseases (such as Crohn’s disease and ulcerative colitis).
• Microbiome modulation: emerging research suggests selenium status can directly influence gut microbial composition. Adequate selenium may support the growth of beneficial bacteria that produce short-chain fatty acids (SCFAs), a key energy source for intestinal cells.
• Nutrient processing: as an antioxidant, selenium helps protect digestive enzymes from damage, supporting efficient food breakdown.

Effects on metabolism and the thyroid

Selenium is closely tied to thyroid function:

• Hormone activation: enzymes that convert inactive thyroid hormone (T4) into its active form (T3) are selenoproteins. Without selenium, metabolism may slow because the body cannot produce enough active hormone, which can contribute to weight gain and low energy.
• Glucose metabolism: there is evidence that selenium participates in insulin signalling, helping cells take up glucose more efficiently, although further research is needed.

Selenium fact – male fertility

Studies indicate selenium may play an important role in improving fertility in men with low selenium status. Selenium is incorporated into the mitochondrial capsule of sperm cells in the form of selenoproteins and may influence sperm function and normal development.

Selenium requirements

According to regulations on food supplements, the recommended intake for adults is 55 µg of selenium per day. The maximum permitted intake under the same framework is 100 µg.

Dietary sources of selenium

The richest sources of selenium are meat and seafood, while selenium levels in plant foods vary widely. Some plants do not require selenium; therefore, selenium content depends largely on the selenium concentration in the soil. A plant grown in selenium-poor soil will contain little selenium, whereas plants grown in selenium-rich soil will contain higher amounts—making average selenium values in plants difficult to estimate.

• Brazil nuts – by far the richest source. Just one to two nuts per day can meet (and even exceed) daily needs. Because high selenium intakes can be toxic, frequent consumption is not recommended.
• Fish and seafood – tuna, cod, sardines and shrimp.
• Meat – veal, turkey and chicken.
• Eggs
• Whole grains – oats and brown rice (if grown in selenium-rich soil).

In foods, selenium occurs mainly as organic compounds—primarily selenomethionine and selenocysteine. Selenomethionine is more common in plant foods, while selenocysteine is predominantly found in animal foods. Inorganic selenium forms include selenides, selenites and selenates, found in vegetables and yeast. In supplements, selenium is typically provided as selenomethionine, selenate or selenite. Selenium compounds are generally well absorbed: absorption of selenite is over 80%, while absorption of selenomethionine and selenate exceeds 90%. However, a significant portion of selenate may be lost in urine before incorporation into tissues, whereas selenite tends to be retained more effectively after absorption.

Selenium is an essential micronutrient whose importance far exceeds its “trace” requirement. Its crucial role in selenoprotein synthesis directly affects thyroid function and the strength of immune responses. Ensuring the recommended daily intake of 55 µg is not only prevention of deficiency—it is meaningful support for the body in combating oxidative stress and maintaining metabolic balance.

References and sources

• EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA). (2014). “Scientific Opinion on Dietary Reference Values for selenium”. EFSA Journal.
• Rayman, M. P. (2012). “Selenium and human health”. The Lancet.
• Kieliszek, M. (2019). “Selenium—Fascinating Microelement, Properties and Sources in Food”. Molecules.
• Nettleford, S. K., Prabhu, K. S. (2018). “Selenium and Selenoproteins in Gut Inflammation and Carcinogenesis”. Nutrients.
• Schomburg, L. (2011). “Selenium, selenoproteins and the thyroid gland: interactions in health and disease”. Nature Reviews Endocrinology.