Nutrient Spotlight- Selenium by Lisa Njoroge, MS, RD, LD

What is it?
If you’ve never heard of selenium, you’re definitely not alone. This little known nutrient is a mineral that is found in various foods and serves many important functions in the body. The recommended daily allowance (RDA) for adults over age 19 is 55 micrograms (mcg) per day. However, slightly more is needed for pregnant (60 mcg/day) or lactating people (70 mcg/day). Selenium deficiency is rare in North America but can be more common in places such as parts of Europe and Asia where there is less selenium in the soil where food is grown (1).
Where can we find it?
Common food sources of selenium include animal proteins such as beef, chicken, turkey, some types of fish, egg, and cottage cheese. Selenium is also found in plant foods like oatmeal, brown rice, beans, lentils, Brazil nuts, bread, and cereals (2).
Why do we need it?
Selenium supports many important functions for humans. It is a crucial part of selenoproteins and enzymes, which act to protect tissues and DNA from free radical damage. Research is being done to learn more about the protective effects of selenium in relation to cancer prevention (2). Selenoproteins have positive effects for cardiovascular health as well by keeping blood platelets from sticking and helping to reduce inflammation (2). Thyroid health is often associated with selenium due to its higher concentration in this gland and effect on thyroid hormone synthesis. Inadequate selenium is one factor that has been found to contribute to the development of autoimmune thyroid conditions (1). This information may lead one to think that more selenium is better, however it is possible to have too much especially when it comes to minerals.
How much?
The tolerable upper intake level (UL) of selenium for all adults is 400 mcg per day (1). Before considering supplementation, it is best to consult your medical provider and/or a Registered Dietitian, who can help to determine how much supplementation, if any, would be appropriate for an individual.
​Most people who have heard of selenium may know that Brazil nuts are widely touted as a good source of this mineral. But as with many foods, the amount of selenium varies widely depending on the mineral content and pH of the soil where the nuts are grown. In fact, one Brazil nut may contain as little as 11% or as much as 288% of the RDA for an adult (3). While it is rare for food sources of nutrients to cause adverse effects from toxicity, Brazil nuts could lead to toxicity if regularly consumed in high amounts.
References:
1. Harvard T.H. Chan School of Public Health. The Nutrition Source: Selenium. https://www.hsph.harvard.edu/nutritionsource/selenium/#:~:text=RDA%3A%20The%20Recommended%20Dietary%20Allowance,and%2070%20micrograms%20daily%2C%20respectively. Accessed 5/28/2022.
2. National Institutes of Health Office of Dietary Supplements: Selenium Fact Sheet for Health Professionals. https://ods.od.nih.gov/factsheets/Selenium-HealthProfessional/ Accessed 5/28/2022.
3. E.C. Silva Junior, et al. Natural variation of selenium in Brazil nuts and soils from the Amazon region. Chemosphere. 2017 Dec;188:650-659. https://doi.org/10.1016/j.chemosphere.2017.08.158.