Selenium and Immune Health

When it comes to supporting immune function, vitamin D often takes centre stage, but selenium is another essential nutrient needed to deal with the aftermath of battling pathogens: oxidative stress. 

What is Selenium?

Selenium is a trace mineral found naturally in soil, water, and many foods¹. Your body only needs it in small amounts, but those small amounts matter significantly. Brazil nuts, seafood, eggs, and whole grains are among the richest dietary sources, though the selenium content of plant-based foods varies considerably depending on the soil in which they were grown².

What Does Selenium Do for Immunity?

Selenium is essential for the production of selenoproteins – a unique family of proteins that regulate thyroid function, and oxidative stress and inflammation throughout the body¹. Here's why that matters for immune health:

Oxidative stress occurs when harmful free radicals accumulate faster than the body can neutralize them³. Chronic oxidative stress damages cells and suppresses immune function, leaving the body less equipped to respond to illness and age-related diseases³. Selenium-dependent enzymes act as a critical line of defense against this process⁴.

Beyond oxidative stress, selenium plays a direct role in supporting both innate and adaptive immune responses. Research has shown that adequate selenium levels support the maturation and proliferation of T-cells – the cells of the immune system responsible for identifying and eliminating pathogens and infected cells. Low selenium levels, by contrast, have been associated with impaired immune cell function and increased susceptibility to viral infections, and autoimmune thyroiditis. 

One mouse study highlighted the importance of selenium and N-acetyl cysteine (NAC) for T-cell and macrophage function by deleting selenoproteins from these cells and observing how they responded to T-cell receptor signaling⁵. Researchers found that selenoprotein-deficient T-cells and macrophages, despite activation, showed reduced mature/functional T-cells, impaired antibody responses, elevated ROS (reactive oxygen species), and poor macrophage migration to inflammation sites⁵. 

Selenium Deficiency: More Common Than You Think

Selenium deficiency is a genuine concern in many parts of the world, including Canada. Because selenium content in food depends heavily on soil selenium content – and Canadian soils are notably selenium-poor in many regions – dietary intake alone may not always be sufficient⁶.

Research has linked selenium deficiency to:

• Increased vulnerability to viral infections
• Greater risk of inflammatory conditions
• Impaired thyroid function, which in turn affects immune regulation
• Slower recovery from illness

Selenium and Viral Infections

One particularly compelling area of selenium research involves its relationship with viral illness. Studies have found that selenium deficiency can cause normally mild viruses to mutate into more virulent strains due to excess ROS levels (oxidative stress), potentially increasing their capacity to cause disease⁷. Adequate selenium levels, conversely, appear to support a more controlled and effective antiviral immune response.

Selenium Toxicity (Selenosis)

As with all things, moderation is key. Selenium toxicity (selenosis) is possible at excessive intake levels, causing symptoms ranging from nausea, diarrhea, fatigue, hair loss, joint pain and nail brittleness to neurological effects such as tremors and myalgia in severe cases^8,9.

The recommended dietary allowance (RDA) for adults is 55 to 70 micrograms per day with an upper tolerable limit of 400 micrograms per day, and 15 to 70 micrograms per day for infants, children and adolescents^10,11.

For anyone concerned about their selenium status, particularly those following restrictive diets, living in selenium-poor regions, or managing chronic health conditions, it is important to test your levels to ensure optimal levels.

Testing and Supplementation

If you're concerned about your selenium levels, speak with your healthcare provider about testing options. Understanding your baseline is the most effective way to determine whether dietary changes or supplementation are appropriate for your individual needs.

At ImmunoCeutica, we believe that informed supplementation – grounded in testing and guided by science – is the foundation of effective immune support. Whether you're looking at vitamin D, selenium, or other key nutrients, knowing your levels is always the first step.

Explore SelNAC — ImmunoCeutica's selenium and N-acetyl cysteine formula for immune defence and antioxidant support.

Learn more about SelNAC → 

References

1. Li, J., Lai, J., Zeng, Y., Zhu, B., & Li, Y. (2025). The relationship between selenium and viral diseases. Interdisciplinary Medicine, 3(2), e20240074. https://doi.org/10.1002/INMD.20240074
2. National Institutes of Health (NIH) Office of Dietary Supplements (ODS). (2025). Selenium [Fact sheet]. https://ods.od.nih.gov/factsheets/Selenium-HealthProfessional/
3. Marrocco, I., Altieri, F., & Peluso, I. (2017). Measurement and Clinical Significance of Biomarkers of Oxidative Stress in Humans. Oxidative Medicine and Cellular Longevity, 2017(1), 6501046. https://doi.org/10.1155/2017/6501046
4. Zoidis, E., Seremelis, I., Kontopoulos, N., & Danezis, G. (2018). Selenium-Dependent Antioxidant Enzymes: Actions and Properties of Selenoproteins. Antioxidants, 7(5), 66. https://doi.org/10.3390/antiox7050066
5. Carlson, B. A., Yoo, M.-H., Shrimali, R. K., Irons, R., Gladyshev, V. N., Hatfield, D. L., & Park, J. M. (2010). Role of selenium-containing proteins in T-cell and macrophage function. Proceedings of the Nutrition Society, 69(3), 300–310. https://doi.org/10.1017/S002966511000176X
6. Canadian Council of Ministers of the Environment. (2009) Canadian soil quality guidelines for the protection of environmental and human health: Selenium. https://ccme.ca/en/res/selenium-canadian-soil-quality-guidelines-for-the-protection-of-environmental-and-human-health
7. Guillin, O., Vindry, C., Ohlmann, T., & Chavatte, L. (2019). Selenium, Selenoproteins and Viral Infection. Nutrients, 11(9), 2101. https://doi.org/10.3390/nu11092101
8. Sutter, M. E., Thomas, J. D., Brown, J., & Morgan, B. (2008). Selenium Toxicity: A Case of Selenosis Caused by a Nutritional Supplement. Annals of Internal Medicine, 148(12), 970–971. https://doi.org/10.7326/0003-4819-148-12-200806170-00015
9. Thomas, L. (2023, March 14). Selenium Toxicity. News Medical. https://www.news-medical.net/health/Selenium-Toxicity.aspx
10. Institute of Medicine (US) Panel on Dietary Antioxidants and Related Compounds. Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium, and Carotenoids. Washington (DC): National Academies Press (US); 2000. 7, Selenium. Available from: https://www.ncbi.nlm.nih.gov/books/NBK225470/
11. Sadler RA, Mallard BA, Shandilya UK, Hachemi MA, Karrow NA. The Immunomodulatory Effects of Selenium: A Journey from the Environment to the Human Immune System. Nutrients. 2024 Sep 30;16(19):3324. https://pubmed.ncbi.nlm.nih.gov/39408290/

This article is provided for educational purposes and does not replace professional medical advice. Always consult a qualified healthcare provider before beginning any new supplement regimen.

 

Reviewed by Niel A. Karrow, Ph.D., Department of Animal Biosciences, University of Guelph