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Inhaltsstoff-Glossar
Selenium
What Is Selenium?
Selenium is an essential trace element that humans must obtain through their diet. Its discoverer named it after the moon goddess Selene because of its silvery appearance. The United States was the first country to recommend selenium intake in 1989.
Selenium follows a U-shaped risk curve: adequate intake is protective, whereas both deficiency and excessive intake increase the risk of conditions such as cancer, diabetes, and cardiovascular disease. Since the body also excretes selenium through the breath, excessive intake or selenium poisoning (selenosis) can cause hair loss, fatigue, and the characteristic "garlic breath."
Selenium follows a U-shaped risk curve: adequate intake is protective, whereas both deficiency and excessive intake increase the risk of conditions such as cancer, diabetes, and cardiovascular disease. Since the body also excretes selenium through the breath, excessive intake or selenium poisoning (selenosis) can cause hair loss, fatigue, and the characteristic "garlic breath."
Where Does Selenium Naturally Occur?
Selenium is a mineral that occurs naturally in the Earth's crust and has also been detected on the Moon and in meteorites. It enters the food chain because plants absorb it from the soil. However, selenium concentrations in soils vary greatly around the world. Some soils contain almost no selenium, while others produce plants and crops with significant selenium levels.
Brazil nuts, seeds, organ meats, and mushrooms are well known for their particularly high selenium content. However, because selenium concentrations vary considerably, obtaining a reliable intake through food alone is difficult. Depending on the region of cultivation and soil composition, a single Brazil nut may provide only a negligible proportion of the daily requirement—or, conversely, potentially toxic amounts of selenium.
For this reason, dietary selenium intake depends primarily on where foods are grown and the selenium content of the soil. European soils are generally considered to be low in selenium. Since 1985, Finland has been the only European country to fortify mineral fertilizers with selenium in order to enrich agricultural soils and foods. As a result, the selenium content of Finnish wheat and onions has increased more than tenfold.
Brazil nuts, seeds, organ meats, and mushrooms are well known for their particularly high selenium content. However, because selenium concentrations vary considerably, obtaining a reliable intake through food alone is difficult. Depending on the region of cultivation and soil composition, a single Brazil nut may provide only a negligible proportion of the daily requirement—or, conversely, potentially toxic amounts of selenium.
For this reason, dietary selenium intake depends primarily on where foods are grown and the selenium content of the soil. European soils are generally considered to be low in selenium. Since 1985, Finland has been the only European country to fortify mineral fertilizers with selenium in order to enrich agricultural soils and foods. As a result, the selenium content of Finnish wheat and onions has increased more than tenfold.
What Is the Primary Function of Selenium in the Body?
The European Food Safety Authority (EFSA) considers it scientifically established that selenium contributes to protection against oxidative stress, the normal function of the immune system, normal thyroid function, and normal spermatogenesis. Adequate selenium status reduces the risk of miscarriage, supports fertility, and promotes healthy thyroid function. Within the thyroid gland, selenium is essential for the activity of the thyroid hormones T3 and T4.
As a component of the amino acid selenocysteine, selenium is crucial for the function of several enzymes, including the selenoprotein glutathione peroxidase. In this role, selenium helps maintain oxidative balance between reactive oxygen species (ROS), which are generated through cellular respiration and environmental influences, and the body's antioxidant defense systems, such as glutathione and dietary vitamin C. This function explains many of the symptoms associated with selenium deficiency and is one reason why selenium requirements may increase in conditions such as AIDS, cancer, or hepatitis. Accordingly, individuals with chronic diseases may potentially benefit from an increased selenium intake.
As a component of the amino acid selenocysteine, selenium is crucial for the function of several enzymes, including the selenoprotein glutathione peroxidase. In this role, selenium helps maintain oxidative balance between reactive oxygen species (ROS), which are generated through cellular respiration and environmental influences, and the body's antioxidant defense systems, such as glutathione and dietary vitamin C. This function explains many of the symptoms associated with selenium deficiency and is one reason why selenium requirements may increase in conditions such as AIDS, cancer, or hepatitis. Accordingly, individuals with chronic diseases may potentially benefit from an increased selenium intake.
What Are the Benefits of Selenium Supplementation?
Because the selenium content of foods varies considerably, selenium intake across the population is often inconsistent. Approximately one-third of Europeans consume too little selenium, making selenium supplementation an important consideration. Scientific reviews indicate that adequate selenium intake may reduce the risk of cancer and cardiovascular disease while also exhibiting anti-inflammatory and antiviral properties.
Recommended selenium intake is based on the concentration of the selenium transport protein in the blood and its relationship with mortality. Researchers assume that the optimal plasma selenium concentration is reached when the selenium transport protein is fully saturated, which occurs at approximately 110–130 micrograms of selenium per liter. However, studies have shown that mortality risk begins to increase again at plasma concentrations exceeding 150 micrograms per liter.
Many people achieve the optimal plasma concentration of 110–130 micrograms per liter by consuming approximately 1 microgram of selenium per kilogram of body weight per day. This corresponds to the intake recommendations of the German Nutrition Society (DGE). The EFSA has established a tolerable upper intake level of 300 micrograms of selenium per day.
The relatively narrow range between optimal selenium status and toxicity—even with only modest excess intake—makes careful dosing essential. Accordingly, the German Federal Institute for Risk Assessment (BfR) recommends a maximum daily intake of 45 micrograms from dietary supplements. Observations in livestock and conflicting findings regarding disease prevention also suggest that excessive selenium intake may increase, rather than reduce, disease risk. For example, while adequate selenium status lowers the risk of developing type 2 diabetes, both very low and very high blood selenium concentrations are associated with an increased risk.
This U-shaped relationship demonstrates that more is not necessarily better. The case of a 50-year-old individual who developed selenium levels up to fifty times above normal, resulting in visual and memory impairment while attempting to strengthen the immune system, clearly illustrates that with selenium, the dose makes the poison.
References
Further information and scientific studies on the active ingredient selenium can be found here.
Selenium and Brain Function: A Poorly Recognized Liaison
www.pubmed.ncbi.nlm.nih.gov/15210302