What is selenium?
Selenium is an essential trace element that, despite its low concentration in the body, plays a crucial role in metabolism, cell protection, the immune system, thyroid function, and fertility . It primarily acts as a component of important enzymes—so-called selenoproteins —which are responsible for antioxidant protection, detoxification, and hormone regulation.
Selenium was only recognized as a vital nutrient in the mid-20th century. Today, it is known to be essential for protecting cells from oxidative stress, regulating the thyroid gland, and strengthening the immune system. Of particular interest is the fact that selenium levels in food are strongly dependent on the soil – in Central Europe, these soils are often low in selenium, which is why a deficiency is relatively common.
Natural sources of selenium include Brazil nuts , fish, seafood, eggs, meat, whole grain products and mushrooms.
How does selenium work?
Selenium exerts its effects mainly via selenoproteins , which are involved in a variety of biological processes.
Cell protection and antioxidants:
Selenium is a component of the enzyme glutathione peroxidase , which neutralizes free radicals and protects cells from oxidative stress. This antioxidant effect plays a crucial role in preventing cell damage, aging processes, and inflammation .
Thyroid function:
Selenium is essential for the conversion of the thyroid hormone thyroxine (T4) into its active form triiodothyronine (T3) . It also protects the thyroid gland from oxidative stress caused by hormone production. Adequate selenium intake is therefore crucial for a healthy metabolism, energy balance, and hormonal equilibrium – especially in combination with iodine .
Immune system:
Selenium increases the activity of immune cells (e.g., lymphocytes and natural killer cells) and promotes antibody production. This can improve the body's defenses against viruses and bacteria and strengthen resistance to infections .
Cardiovascular system:
Due to its antioxidant properties, selenium protects blood vessels from oxidative damage and thus contributes to maintaining healthy heart function . Studies suggest that adequate selenium intake in combination with vitamin E can reduce the risk of cardiovascular disease.
Fertility and reproduction:
Selenium supports the production of healthy sperm and protects them from oxidative damage. In women, it plays a role in egg maturation and pregnancy.
Skin, hair and nails:
Selenium contributes to the maintenance of normal hair and nails, as it is involved in the formation of keratin and protects skin cells from oxidative stress.
Benefits of selenium
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It acts as a powerful antioxidant and protects cells from free radicals.
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Supports thyroid function and hormone production
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Strengthens the immune system and the body's defenses
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Promotes heart health and prevents vascular damage
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Supports fertility and reproduction in men and women
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Contributes to the maintenance of healthy hair, skin and nails
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Works synergistically with vitamin E to protect cells
Possible side effects and interactions
Selenium is essential for life in small amounts, but can be toxic in excessive doses. The recommended daily intake is approximately 55–70 µg for adults. Prolonged intake exceeding 300–400 µg daily can lead to selenosis – a poisoning that can manifest as hair loss, brittle nails, skin irritation, fatigue, garlic-like breath, or stomach problems.
People with thyroid disorders should only take selenium supplements after consulting their doctor, especially if they are already using iodine or thyroid hormones.
The combination of selenium and vitamin E is considered particularly effective, as both nutrients regenerate each other and together provide antioxidant cell protection.
Conclusion
Selenium is a small trace element with a big impact. It protects cells, strengthens the immune system, regulates the thyroid gland, and supports healthy skin, hair, nails, and fertility. An adequate supply is crucial for energy, vitality, and hormonal balance. Since many soils in Europe are low in selenium, targeted supplementation—especially in combination with vitamin E—can be beneficial for long-term protection of body and mind against oxidative stress and metabolic disorders.
Sources
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Rayman MP. (2012): Selenium and human health. Lancet , 379(9822), 1256–1268.
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Drutel A, Archambeaud F, Caron P. (2013): Selenium and the thyroid gland: more good news for doctors. Clin Endocrinol (Oxf) , 78(2), 155–164.
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Steinbrenner H, et al. (2015): Functions of selenoproteins and biomarkers of selenium status. Antioxid Redox Signal , 23(10), 814–828.
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Fairweather-Tait SJ, et al. (2011): Selenium in human health and disease. Antioxid Redox Signal , 14(7), 1337–1383.