Selenium is a recently discovered mineral that is necessary for thyroid function, DNA production, reproductive health, and may also decrease risk for cancer and heart disease as it is thought to protect against toxins and free radicals by activating vitamin C and lowering LDL cholesterol (McGuire et al., 2018, National Institutes of Health, 2019). Selenium also works best as an antioxidant when combined with vitamin E, which can help to neutralize free radicals (St. Luke’s Hospital, 2015). Some of the best food sources are Brazil nuts, seafood, meat, poultry, eggs, bread, and other grains especially when fortified with selenium. Selenium is also found in vegetables like broccoli, spinach, beans, and potatoes, but the amount varies based on the amount present in the soil where these vegetables are grown (NIH, 2019).
Selenium is mainly absorbed in the duodenum and the cecum of the small and large intestines - only a small amount is absorbed before reaching the small intestine (Youcef et al., 2013). Calcium, iron, and sulfur are other minerals which have been found to decrease the absorption of selenium. However, this doesn’t mean that selenium is not absorbed at all when consumed with foods that contain these minerals like dairy, meat, and legumes. It just means that one doesn’t absorb as much due to “steric competitiveness” (Youcef et al., 2013).
The RDA for selenium is 55 micrograms/day and the upper limit is 400 micrograms/day for adults (McGuire et al., 2018). For most people consuming a healthy and varied diet, supplementation of selenium is unnecessary. However, it has been found that smoking, alcohol intake, birth control pills, and health conditions that prevent proper absorption of nutrients such as Crohn’s and ulcerative colitis impact selenium levels (St. Luke’s Hospital, 2015). Additional vitamins and supplements may need to be used to avoid depletion of nutrients including selenium, zinc, calcium, magnesium, and phosphate especially when smoking and alcohol intake are combined (Lloyd et al., 1983). When this study was completed in 1983, the mechanism of action was unknown, but it has since been found that alcohol intake inhibits the breakdown of nutrients thereby impairing nutrient absorption (NIH, 2000). Similar malabsorption problems have been found with smoking and oral contraceptive use (Palmery et al., 2013, Preston, 1991).
Studies have also found that there may be a higher rate of cancer and heart disease in those that do not consume adequate amounts of selenium and conversely a lower incidence when there is an adequate amount consumed, but it is not completely understood how (NIH, 2019). Also, if a deficiency develops, this may lead to a weakened immune system, hair loss, fatigue, muscle weakness, and/or infertility (St. Luke’s Hospital, 2015). Finally, not so relevant in the U.S. is Keshan’s disease, which is the result of a severe selenium deficiency. There is a specific region of China where there is little selenium found in the soil, so the crops grown in that environment become deficient as well. This has been known to lead to serious and potentially fatal heart problems especially in children (McGuire et al., 2018).
References
Lloyd, B., Lloyd, R. S., & Clayton, B. E. (1983). Effect of smoking, alcohol, and other factors on the selenium status of a healthy population. Journal of epidemiology and community health, 37(3), 213–217. https://doi.org/10.1136/jech.37.3.213
McGuire, M., & Beerman, K. (2018). Nutritional Sciences: From Fundamentals to Food (3rd ed.). Boston, MA: Cengage Learning.
National Institutes of Health. (2000). Alcohol Alert. Retrieved from: https://pubs.niaaa.nih.gov/publications/aa22.htm
National Institutes of Health. (2019). Selenium. Retrieved from: https://ods.od.nih.gov/factsheets/Selenium-Consumer/#:~:text=Selenium%20is%20a%20nutrient%20that,free%20radicals%20and%20from%20infection
Palmery, M., Saraceno, A., Vaiarelli, A., Carlomagno., G. (2013). Oral contraceptives and changes in nutritional requirements. Eur Rev Med Pharmacol Sci. 17(13):1804-1813.
Preston, A. (1991). Cigarette smoking-nutritional implications. Prog Food Nutr Sci. 15(4):183-217.
St. Luke’s Hospital. (2015). Selenium. Retrieved from: https://www.stlukes-stl.com/health-content/medicine/33/000325.htm
Youcef, M., Hornick, J., Istasse, L., Dufrasne, I. (2013). Selenium in the Environment, Metabolism and Involvement in Body Functions. Molecules.18, 3292-3311 https://www.mdpi.com/1420-3049/18/3/3292