Selenium: The Little-Known Mineral That Packs a Big Punch for Health


Selenium is an essential mineral that is vital to maintaining good health. This trace element is present in small amounts in the body and plays a critical role in various physiological processes, including immune function and antioxidant defense. While selenium deficiency is relatively rare in developed countries, it can have serious health consequences, including increased risk of certain cancers, thyroid disease, and cognitive decline. On the other hand, excessive selenium intake can also be harmful, leading to toxicity and other adverse effects. Therefore, it is important to maintain a balanced intake of selenium through a healthy and varied diet.

Brief History and Discovery

Selenium was first discovered by Jöns Jacob Berzelius in 1817 while he was analyzing residues left after the production of sulfuric acid. He named the element after the Greek word "selene," which means moon because it had properties similar to tellurium, which was named after the Latin word "tellus," which means earth.Selenium was initially regarded as a toxic element, but its essentiality for animal nutrition was recognized in the 1950s when it was found to be an essential component of glutathione peroxidase, an enzyme that protects cells from oxidative damage.


Brazil nuts are one of the richest sources of selenium, containing over 100 micrograms of selenium per nut. Just one nut can provide you with your daily recommended intake of selenium. Brazil nuts also contain other beneficial nutrients, such as magnesium, copper, and zinc. However, it's important to note that consuming too many Brazil nuts can lead to selenium toxicity, which can cause nausea, diarrhea, and hair loss.

Seafood is another excellent source of selenium, particularly tuna, halibut, and shrimp. Tuna is one of the best sources, with 3 ounces of tuna providing around 68 micrograms of selenium. Halibut and shrimp are also good sources, with 3 ounces of halibut providing around 47 micrograms of selenium, and 3 ounces of shrimp providing around 40 micrograms of selenium.

Meat and poultry are also good sources of selenium. Beef, chicken, and turkey are some of the most commonly consumed meats that contain selenium. A 3-ounce serving of beef provides around 33 micrograms of selenium, while a 3-ounce serving of chicken or turkey provides around 20 micrograms of selenium. However, it's important to choose lean cuts of meat to avoid consuming excess fat and cholesterol.

Whole grains, such as brown rice and whole wheat bread, are also good sources of selenium. While the amount of selenium in whole grains may not be as high as in other sources, they can still contribute to your daily selenium intake. One slice of whole wheat bread provides around 6 micrograms of selenium, while a cup of brown rice provides around 19 micrograms of selenium.

Dairy products such as milk, cheese, and yogurt contain small amounts of selenium. One cup of milk provides around 8 micrograms of selenium, while one slice of cheddar cheese provides around 6 micrograms of selenium. While dairy products can contribute to your daily selenium intake, it's important to choose low-fat or non-fat options to avoid consuming excess fat and cholesterol.

In addition to food sources, selenium supplements are also available. However, it's important to be cautious when taking supplements, as excessive selenium intake can be toxic. The recommended daily intake of selenium is 55 micrograms for adults, and taking more than 400 micrograms per day can lead to selenium toxicity.

Functions in the Body

Selenium is an essential mineral that plays a critical role in many bodily functions. It acts as a cofactor for enzymes involved in antioxidant defense, thyroid hormone metabolism, DNA synthesis, and immune function.

One of the primary functions of selenium is its role as a component of glutathione peroxidase, an enzyme that protects cells from oxidative damage by neutralizing harmful free radicals. Selenium also plays a critical role in immune function by enhancing the activity of immune cells and promoting the production of antibodies.

Selenium is also important for thyroid health, as it is required for the conversion of the inactive form of thyroid hormone (T4) to the active form (T3). Additionally, selenium is involved in DNA synthesis and repair, which is essential for proper cellular function and growth.

Recommended Daily Intake

Individuals of different ages, sexes, and health conditions have different selenium RDAs. There should be no more than 55 micrograms of selenium in an adult's daily diet, as stated by the National Institutes of Health. The ideal selenium intake, however, may differ from one person to the next, based on factors like food, lifestyle, and current health state. An excessive consumption of selenium can be dangerous, so it's best to consult a doctor before starting selenium supplementation.

Recap and Conclusion

Many biological activities, such as immunological function and antioxidant defense, rely on the trace element selenium. Selenium deficiency is not common, but it can lead to major health problems like cancer, thyroid problems, and mental deterioration. Selenium has many beneficial properties, yet it is potentially hazardous in high doses. Therefore, a diet rich in selenium-containing foods, such as brazil nuts, seafood, and whole grains, should be maintained for optimal health. Consult your doctor or a certified nutritionist to decide if selenium supplementation is essential if you are concerned about your selenium levels or have a medical condition that affects selenium absorption. The immune system and general health can both benefit from taking measures to increase selenium consumption.

Aaron Bernstein, MD, MPH

Aaron Bernstein is the Interim Director of The Center for Climate, Health, and the Global Environment, a pediatrician at Boston Children’s Hospital, and an Assistant Professor of Pediatrics.

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