Selenium: The Small Mineral with a Big Impact

Selenium is a trace mineral that is required for optimal health. This mineral plays many vital roles in several bodily processes. Selenium is not stored in the body for long periods, so regular intake of the mineral is necessary for homeostasis (Bai, et. al., 2025). Achieving the proper balance of selenium is pivotal in supporting long term health, since too much and too little can have devastating health consequences. Testing and dietary changes can help you find the right balance of selenium and achieve long term wellness.

Selenium is used in the body as a component of several enzymes and proteins, many of which serve as antioxidants (The Nutrition Source, 2023; National Institute of Health, 2025; Kubala, 2023; Griffin, et. al., 2025; Bai, et. al., 2025). Free radicals are produced as a byproduct of cellular metabolism and cause cellular and DNA damage if they’re left to roam the body. Antioxidants play a key role by neutralizing these compounds and thereby reduce the rate of cellular aging and lower inflammation levels. Selenium is just one of many antioxidants. Eating a diet rich in a variety of vegetables, nuts, seeds, and fruits ensures that you consume a wide array of antioxidant compounds as well as necessary vitamins and minerals.

The immune system relies on selenium for “cellular immunity, humoral immunity, and nonspecific immune functions” (Bai, et. al., 2025). Both the nonspecific and specific aspects of the immune system are weakened when selenium is deficient. Glutathione peroxidase supports macrophage function and is dependent upon selenium. Macrophages remove pathogens from the body. Selenium is also key in lymphocyte function, which in turn supports immunoglobulin production (Bai, et. al., 2025). Proper selenium intake can help support immune system health, especially in people with deficiencies.

People with both low and high selenium intakes and selenium levels are at increased risk for cardiovascular disease. Selenoproteins, which are reliant on selenium, protect cell membranes and prevent platelets from becoming “sticky.” These effects, as well as the antioxidant role that selenium plays, help prevent heart disease (The Nutrition Source, 2023). 

Selenium supports male fertility, as severe deficiencies can cause male infertility and low sperm quality (Bai, et. al., 2025; Griffin, et. al., 2025). If you are planning to conceive, it would be wise to have your or your spouse’s selenium levels tested to ensure that selenium intake is adequate.

The highest concentration of selenium in the body is in the thyroid gland (The Nutrition Source, 2023). The thyroid depends on selenium for thyroid hormone regulation and synthesis, as well as the conversion of T4 to T3 (Bai, et. al., 2025). Low selenium can lead to autoimmune thyroid conditions and increased risk of thyroid disease, especially in women (The Nutrition Source, 2023; National Institute of Health, 2025). However, supplements have not yet been proven to be effective in influencing thyroid function (The Nutrition Source, 2023). Luckily, there are a variety of foods that contain bioavailable selenium.

According to the National Institute of Health, chronic selenium deficiencies are linked to cognitive decline (2025). Therefore, maintaining proper levels of selenium can prevent cognitive decline, as well as neurodegenerative diseases (Kubala, 2023; Bai, et. al., 2025). Maintaining a balanced selenium intake can help you maintain long term cognitive health.

Selenium may also reduce your risk of cancer. One study compared those with the lowest selenium levels and intakes and people with the highest selenium levels and intakes and found a 31% reduced risk of cancer and a 45% reduce risk of death from cancer in people with the highest selenium levels and intakes (The Nutrition Source, 2023). In a later article, Bai, et. al. reported that “selenium has been proven to prevent tumor occurrence” (2025). Maintaining optimal selenium levels can help you prevent and recover from cancer.

Selenium levels can be tested through a blood test. The ideal blood level falls between 80-140 ng/mL (Bai, et. al., 2025). If you have a high level of selenium, stop taking supplements that contain selenium or reduce your dietary intake. If your selenium is low, increase your dietary intake for a few months then retest your level before considering supplements. Selenium supplements raise the risk for toxicity and long term use has been linked to a high risk of type 2 diabetes. Taking high dose selenium supplements can also cause iodine deficiency. The established RDA, which is the bare minimum, is 55 micrograms of selenium daily. The UL, which is the safe upper limit, is 400 micrograms per day (The Nutrition Source, 2023). The best way to ensure that you’re getting the right amount of selenium is through dietary changes. 

The foods richest in selenium include:

• oysters

• Brazil nuts

• halibut

• yellowfin tuna

• eggs

• sardines

• sunflower seeds

• chicken breast

• shiitake mushrooms

• beef

• turkey

• chicken

• beans

• lentils

• shrimp

• cottage cheese

(Kubala, 2023; The Nutrition Source, 2023; National Institute of Health, 2025).

It’s important to note that the actual amount of selenium in these foods varies based on the soil content where the food was grown, so incorporating a variety of these foods is the best way to ensure your selenium requirement is being met (Bai, et. al., 2025). If your selenium level is elevated, reduce your consumption of these foods.

Overcoming deficiencies and toxicities can be a slow process, but it is well worth the long term health improvements. Schedule an appointment with Renewed Hope Nutrition to receive functional lab interpretations, personalized nutrition recommendations, and holistic health recommendations.

References:

Bai, S., Zhang, M., Tang, S., Li, M., Wu, R., Wan, S., Chen, L., Wei, X., & Feng, S. (2025). Effects and Impact of Selenium on Human Health, A Review. Molecules, 30(1), 50. https://doi.org/10.3390/molecules30010050

Griffin, R. M., Key, A. P., & Cameron, K. (August 3, 2025). Selenium: What are the Benefits, Sources, & Risks. WebMD. Retrieved from https://www.webmd.com/a-to-z-guides/supplement-guide-selenium

Kubala, J. (February 6, 2023). 7 Science-Based Health Benefits of Selenium. Healthline: Nutrition. Retrieved from https://www.healthline.com/nutrition/selenium-benefits

National Institute of Health. (September 4, 2025). Selenium: Fact Sheet for Health Professionals. Retrieved from https://ods.od.nih.gov/factsheets/Selenium-HealthProfessional/

The Nutrition Source. (March 2023). Selenium. Harvard T.H. Chan School of Public Health. Retrieved from https://nutritionsource.hsph.harvard.edu/selenium/