The Benefits of Selenium: Why You Need This Mineral In Your Diet For Healthy Aging
The mineral selenium is often under-recognized despite being a vital nutrient for human health. Selenium benefits several organs and systems in the body, ranging from heart health to cognition to thyroid support. In this article, read about the top five benefits of selenium for healthy aging, where to find selenium in foods, and what forms of selenium supplements you can take.
What is Selenium?
Selenium is a trace mineral found in many foods. Humans cannot make selenium in the body, making it nutritionally essential to consume in the diet. There are two forms of selenium: the organic forms selenomethionine and selenocysteine, and the inorganic forms selenate and selenite. In human and animal tissues, selenium is primarily stored as selenomethionine.
Selenium’s health benefits come from a family of proteins called selenoproteins, which are made up of selenocysteine. Approximately 25 of these proteins act as enzymes in the human body, performing various physiological functions.
Selenium Food Sources, Deficiency, and Toxicity
The best dietary sources of selenium are Brazil nuts, tuna, shrimp, halibut, sardines, and organ meats. Good sources of selenium include other fish and shellfish, meat, dairy, eggs, and some whole grains, like whole-wheat bread and brown rice.
Although selenium is present in many foods, concentrations of the mineral can vary widely based on the soil of some geographical regions. Regions with poor soil selenium content will have lower selenium levels in the plants and animals grown or raised there.
The Recommended Dietary Allowance (RDA) for all non-pregnant or lactating adults is 55 mcg of selenium per day. For reference, just one Brazil nut contains 90-95 mcg, exceeding your daily needs for the mineral. If Brazil nuts are consumed chronically, and in excess, one may experience signs of selenium toxicity, as the tolerable Upper Level for selenium is 400 mcg per day.
Selenium deficiency can be induced by various stressors, including infectious disease, malnutrition, or oxidative damage. Groups at increased risk of selenium deficiency include those living in areas with low access to selenium-rich foods — including many African and Asian countries — people undergoing kidney dialysis, and people with HIV.
Selenium toxicity, also known as selenosis, can cause a metallic taste in the mouth, garlicky breath, brittle hair and nails, gastrointestinal distress, skin rashes, fatigue, and nervous system abnormalities.
Top 5 Health Benefits of Selenium
1.Selenium Has Antioxidant Properties
Many of selenium’s health benefits stem from its status as a powerful antioxidant. The enzyme glutathione peroxidase (GPx), which is also a selenoprotein, is well known for its antioxidant abilities.
GPx and other selenoproteins have been found to protect the body against pharmaceutical drug toxicity, environmental pollutants, heavy metal exposure, and damage to cells and DNA. This cellular damage comes from oxidative stress caused by an accumulation of free radicals and reactive oxygen species (ROS).
Antioxidants’ primary function is to scavenge for these harmful and inflammatory molecules. The GPx family has been found to neutralize the reactive oxygen species of superoxide, hydrogen peroxide, hydroxyl radicals, and peroxynitrite.
In a study published in Lipids in Health and Disease in December 2009, rats eating a high-fat diet who received supplemental selenium experienced a 29% decrease in ROS levels compared to rats without selenium.
Three other compounds found in selenium that function as antioxidants are selenoprotein P, thioredoxin reductase, and iodothyronine deiodinases.
High levels of ROS and free radicals promote inflammation and play a role in various chronic diseases, including cardiovascular and neurodegenerative diseases.
2. Selenium Supports Heart Health
Selenium is involved in several cardiometabolic processes, indicating that adequate levels of the mineral are associated with improved heart health.
There are many diseases associated with poor cardiovascular health, including atherosclerosis, hypertension, dyslipidemia, heart disease, heart attack, and type 2 diabetes.
Many of these cardiometabolic conditions are caused, in part, by high levels of cardiac and vascular oxidative damage. Therefore, the high antioxidant capacity of selenium and selenoproteins may mitigate these damaging compounds and improve heart health, as discussed in a May 2015 review published in Nutrients.
In a study published in PLoS One in June 2015, higher dietary intakes of selenium were associated with a reduced risk of metabolic syndrome, which is a cluster of five conditions that increase the risk for heart disease. The five conditions are excess abdominal adiposity, high blood pressure, high blood sugar, and abnormal cholesterol and triglyceride levels.
However, too much selenium is not a good thing. Some research has found that people with the highest blood levels of selenium are at an increased risk of developing type 2 diabetes or high cholesterol. Therefore, a moderate intake of selenium is recommended.
3. Selenium Supports Brain Health
Adequate intake of selenium may support brain health — again, through its ability to reduce oxidative damage, which is an underlying cause of many neurodegenerative disorders.
Selenium and its associated selenoproteins are involved with the proper functioning of neurons, astrocytes, and microglia, which are specialized cells that support the brain and central nervous system.
Research has indicated that low levels of selenium in the brain are linked to cognitive decline. As discussed in an August 2015 review published in Biometals, the various forms of selenium and selenoproteins have been found to reduce neuroinflammation and inhibit the accumulation of beta-amyloid and tau proteins. Aggregates of beta-amyloid and tau proteins are indicative of Alzheimer’s disease progression.
In a small study published in the European Journal of Nutrition in February 2016, older adults with mild cognitive impairment who consumed one Brazil nut per day for six months experienced increases in blood selenium and GPx levels and improved cognition.
Although not all studies have shown a reduced risk of AD with selenium supplements, most research points towards selenium benefiting the brain through a reduction in inflammation and oxidative damage.
4. Selenium Supports Thyroid Health
In the human body, the thyroid, which is the small butterfly-shaped gland that regulates metabolism, contains the highest amount of selenium per gram of tissue and the highest quantity of selenoproteins.
Selenium is essential for producing thyroid hormone. The mineral iodine is also necessary for synthesizing thyroid hormone, and iodine requires selenium to do so. Research has found that selenium deficiency decreases thyroid hormone synthesis. This is because the selenoprotein iodothyronine deiodinase is responsible for converting the inactive form of thyroid hormone (T4) into its active form (T3).
GPx is particularly vital for thyroid health, as the antioxidant enzyme removes harmful free radicals produced during the thyroid hormone conversion process.
Although selenium is essential for thyroid health, it does have a U-shaped relationship, meaning that both too low and too high levels of the mineral are associated with adverse thyroid health outcomes. Therefore, a moderate and balanced intake of selenium is necessary for optimal health.
5. Selenium Supports Immune Health
Selenium exhibits antibacterial and antiviral activity, which could help the immune system fight off illness-causing pathogens.
In general, selenium stimulates the immune system, as the mineral upregulates the growth and activity of T-helper cells, B-cells, and natural killer cells while reducing inflammatory cytokines.
Selenium deficiency may be implicated in cases of viral and bacterial infections. As discussed in a January 2015 review published in Advances in Nutrition, one study found that children infected with influenza A virus were more likely to have low plasma selenium levels.
Other research with animals found that selenium-deficient mice infected with the H1N1 virus had a 75% mortality rate compared to 25% in selenium-sufficient mice.
The authors indicate that supplemental selenium up to 200 mcg per day may be an accessible way to prevent or improve outcomes with viral or bacterial infections.
Selenium Supplements: Types, Safety, and How to Use
As mentioned, too much selenium is not a good thing. Most supplements contain about 200 mcg, which is considered a safe daily dosage.
Selenium has several different forms. You may see selenomethionine, selenocysteine, selenate, or selenite on the label.
At the very least, ensure the selenium supplement contains both selenocysteine and selenomethionine, as selenocysteine makes up the selenoproteins, and selenomethionine is absorbed most easily. A combination of all the forms of selenium allows for optimized heart, brain, thyroid, and immune support.
- Selenium is an essential mineral found in many foods and can be taken supplementally to support the cardiovascular system, brain, thyroid, and immune system.
- However, selenium is a double-edged sword: both too little and too much of the mineral is harmful to health.
- Consuming selenium-rich foods — but not over-eating Brazil nuts — or taking 200 mcg of supplemental selenium appears to be generally safe and supportive to health.
Aaseth J, Alexander J, Bjørklund G, et al. Treatment strategies in Alzheimer's disease: a review with focus on selenium supplementation. Biometals. 2016;29(5):827-839. doi:10.1007/s10534-016-9959-8
Benstoem C, Goetzenich A, Kraemer S, et al. Selenium and its supplementation in cardiovascular disease--what do we know?. Nutrients. 2015;7(5):3094-3118. Published 2015 Apr 27. doi:10.3390/nu7053094
Kaur HD, Bansal MP. Studies on HDL associated enzymes under experimental hypercholesterolemia: possible modulation on selenium supplementation. Lipids Health Dis. 2009;8:55. Published 2009 Dec 16. doi:10.1186/1476-511X-8-55
Kiełczykowska M, Kocot J, Paździor M, Musik I. Selenium - a fascinating antioxidant of protective properties. Adv Clin Exp Med. 2018;27(2):245-255. doi:10.17219/acem/67222
Kohler LN, Florea A, Kelley CP, et al. Higher Plasma Selenium Concentrations Are Associated with Increased Odds of Prevalent Type 2 Diabetes. J Nutr. 2018;148(8):1333-1340. doi:10.1093/jn/nxy099
Office of Dietary Supplements - Selenium. NIH Office of Dietary Supplements. https://ods.od.nih.gov/factsheets/Selenium-HealthProfessional/ Published March 2020.
Prabhu KS, Lei XG. Selenium. Adv Nutr. 2016;7(2):415-417. Published 2016 Mar 15. doi:10.3945/an.115.010785
Rita Cardoso B, Apolinário D, da Silva Bandeira V, et al. Effects of Brazil nut consumption on selenium status and cognitive performance in older adults with mild cognitive impairment: a randomized controlled pilot trial. Eur J Nutr. 2016;55(1):107-116. doi:10.1007/s00394-014-0829-2
Steinbrenner H, Al-Quraishy S, Dkhil MA, Wunderlich F, Sies H. Dietary selenium in adjuvant therapy of viral and bacterial infections. Adv Nutr. 2015;6(1):73-82. Published 2015 Jan 15. doi:10.3945/an.114.007575
Tinggi U. Selenium: its role as antioxidant in human health. Environ Health Prev Med. 2008;13(2):102-108. doi:10.1007/s12199-007-0019-4
Ventura M, Melo M, Carrilho F. Selenium and Thyroid Disease: From Pathophysiology to Treatment. Int J Endocrinol. 2017;2017:1297658. doi:10.1155/2017/1297658
Wang N, Tan HY, Li S, Xu Y, Guo W, Feng Y. Supplementation of Micronutrient Selenium in Metabolic Diseases: Its Role as an Antioxidant. Oxid Med Cell Longev. 2017;2017:7478523. doi:10.1155/2017/7478523
Wei J, Zeng C, Gong QY, Li XX, Lei GH, Yang TB. Associations between Dietary Antioxidant Intake and Metabolic Syndrome. PLoS One. 2015;10(6):e0130876. Published 2015 Jun 22. doi:10.1371/journal.pone.0130876
Yu L, Sun L, Nan Y, Zhu LY. Protection from H1N1 influenza virus infections in mice by supplementation with selenium: a comparison with selenium-deficient mice. Biol Trace Elem Res. 2011;141(1-3):254-261. doi:10.1007/s12011-010-8726-x