Selenium is a trace mineral essential to our health and wellbeing. Among many other important roles in our body, it contributes to DNA synthesis, boosts our immune system and keeps our thyroid health in check. Selenium may also protect us from a host of chronic diseases. At the same time, high doses of this mineral can be toxic. As such, you may be wondering whether it is actually a good idea to supplement it.
It needs to be pointed out that selenium is a relative newcomer to the nutrition world, and we are still learning more about it. This trace mineral was only discovered as an element in 1817 by the Swedish chemist Jöns Jacob Berzelius. What’s more, it took many years before we discovered that it can be beneficial to our health, with scientists only determining it as an essential nutrient in the 1950s.
Here, we discuss what selenium is, where to find it, and what the science says about its effects on various aspects of our health.
Why do we need selenium?
Selenium is an essential trace mineral, but unlike other minerals including calcium, potassium or magnesium, our bodies don’t need high amounts of it. Selenium is an essential component of various enzymes and proteins called selenoproteins. Selenoproteins play numerous roles in our body, from helping to make DNA to protecting against cell damage.
According to the Hormones (opens in new tab) journal, the health effects of selenium have often been characterized by a U-shaped relationship. That is, both low and high doses of this trace mineral can increase mortality. Certain individuals may tolerate lower or higher intakes better than others, while exposure to a high selenium intake from a very young age may alter the composition of the gut microbes, which in turn can reduce its toxicity.
One of the most researched aspects of selenium is its effect on the immune system. According to the Nutrients (opens in new tab) journal, selenoproteins play a crucial role in regulating our immune responses and inflammation levels, mostly through their ability to bring down oxidative stress levels. Not getting enough selenium may increase our susceptibility to viral infections and slow down our recovery.
The evidence is also emerging that selenium deficiency may be linked to autoimmune diseases, as reported in the International Journal of Molecular Sciences (opens in new tab). This trace element has been shown to contribute to the management of complications of these conditions, and even improved chances of patients’ survival. However, more studies are needed to fully understand these associations.
Selenium is critical for the proper functioning of the thyroid gland. In fact, this organ has the highest concentration of selenium in the human body. Thyroid releases several important hormones involved in metabolism control, such as thyroxine and triiodothyronine. Without enough selenium, these hormones cannot be synthesized, and the gland itself does not work properly.
Selenium supplementation may play a role in several thyroid disorders. According to a review published in the Thyroid (opens in new tab) journal, it can decrease circulating thyroid autoantibodies in patients with chronic autoimmune thyroiditis, a condition that often leads to an underactive thyroid.
Selenium may also play a role in cardiovascular health. According to the Nutrients (opens in new tab) journal, selenoproteins like glutathione peroxidase and thioredoxin reductase may be crucial to protecting our heart and veins from the damaging effects of free radicals.
A study in the International Journal of Molecular Sciences (opens in new tab) has also linked selenium deficiency to an increased risk of developing heart attacks, heart failure, coronary heart disease, and atherosclerosis. Having said this, a meta-analysis published in the Journal of Trace Elements in Medicine and Biology (opens in new tab) suggests that supplementation alone may not be enough to reduce the risk of dying from coronary heart disease.
Due to its strong antioxidant properties, selenium may help protect the skin against free radicals and photodamage. This trace mineral is also important for skin regeneration and proper wound healing.
More recently, scientists have been exploring the link between selenium and gut health. According to the Frontiers in Nutrition (opens in new tab) journal, gut bacteria may improve the bioavailability of this trace mineral in our digestive system. At the same time, selenium may be crucial to balancing our gut microbiota, and not getting enough of it may result in an increased number of bacteria linked to cancers, thyroid dysfunction, inflammation, and cardiovascular disorders.
A low intake of selenium may increase the risk of asthma, as reported in the Public Health Nutrition (opens in new tab) journal. Since asthma has been linked to increased levels of oxidative stress, scientists suggest that selenium’s antioxidant properties may be at the center of this protective mechanism. However, more research is needed to understand its exact nature.
Selenium may also be important for our reproductive health. A review in the Nutrients (opens in new tab) journal links low selenium intake to infertility. Multiple studies (opens in new tab) also suggest that this trace mineral may be particularly essential for sperm production. However, it is not clear which form or how much selenium is needed to boost reproductive health.
The evidence is growing that selenium may be important for the proper functioning of our nervous system. As reported in the Frontiers in Neuroscience (opens in new tab) journal, this trace mineral may have a protective role against psychological stress. Chronic stress can lead to increased production of glucocorticoid hormones, which in turn can cause memory problems, emotional distress and a host of physical symptoms. Selenium appears to mitigate the effects of these hormones on the brain.
How much selenium should you consume?
According to the National Institutes of Health (opens in new tab), the Daily Value (DV) for adult men and women aged 19 or over is 55 micrograms (mcg, μg) daily.
The Recommended Dietary Allowance (RDA) for pregnant and lactating women is 60 and 70 micrograms daily, respectively.
It also needs to be stressed that the Tolerable Upper Intake Level (UL) for selenium for all adults is 400 micrograms daily. High selenium consumption may result in acute toxicity. The main symptoms include vomiting, diarrhea, abdominal pain and nausea. In severe cases, selenium overdose may lead to breathing problems and can be fatal.
What are the best sources of selenium?
According to the Harvard School of Public Health (opens in new tab), the amount of selenium in foods can vary widely depending on the selenium content of the soil in which it is grown. Plant foods obtain selenium from soil, which will then affect the amount of selenium in animals eating those plants. In general, animal-based foods tend to be good sources.
The best food sources of selenium include:
- Brazil nuts: 544.4μg (990% DV) per 1oz handful / 1917μg (3485% DV) per 100g
- Tuna: 183.9μg (334% DV) per 6oz fillet / 108.2μg (197% DV) per 100g
- Shellfish: 130.9μg (238% DV) per 3oz serving / 154μg (280% DV) per 100g
- Lean pork chops: 80.6μg (147% DV) per 6oz serving / 47.4μg (86% DV) per 100g
- Beef steak: 61.2μg (111% DV) per 6oz serving / 36μg (65% DV) per 100g
- Chicken breast: 54.2μg (99% DV) per 6oz serving / 31.9μg (58% DV) per 100g
- Firm tofu: 43.8μg (80% DV) per cup / 17.4μg (32% DV) per 100g
- Whole wheat pasta: 42.5μg (77% DV) per cup / 36.3μg (66% DV) per 100g
What are the symptoms of selenium deficiency?
According to the Harvard School of Public Health (opens in new tab), the main symptoms of selenium deficiency include:
- Nausea and vomiting
- Altered mental state and confusion
Three diseases are strongly linked to selenium deficiency:
- Keshan disease: Occurs only in children, main symptoms include enlarged heart and poor cardiovascular function
- Kashin-Beck disease: Occurs in children and adolescents, main symptoms include deformed bones and joints of the hands and fingers, elbows, knees, and ankles
- Myxedematous endemic cretinism: Occurs in children born to mothers deficient in both selenium and iodine, results in developmental issues
Groups at risk for selenium deficiency include:
- People living in low-selenium regions who also eat a primarily plant-based diet, such as some populations in China, Russia, and Europe
- People following highly restrictive and/or unbalanced plant-based diets
- People with HIV
- People with kidney failure undergoing dialysis
According to the Centers for Disease Control and Prevention (opens in new tab), selenium deficiency in the U.S. is rare, and most cases are either a direct result of gastrointestinal problems or the surgical removal of part of the stomach.