Selenium (Se) may be a lesser-known mineral for many, but that doesn't diminish its incredible benefits. It's a vital nutrient that helps support your body's immune response. In fact, selenium is the star of at least 25 selenoproteins; compounds that regulate human immune cell function. Scientists have discovered that inadequate selenium and the ability to create these selenoproteins, can lead to immune and inflammation-based diseases.1
Summary of selenium and immune responses. Figure 1: Nutrients. 2018 Sep; 10(9): 1203.
But this antioxidant does a lot more than protecting our cells from oxidative damage, like helping repair DNA and supporting thyroid hormone metabolism.2,3
Selenium’s Role in Sustaining Our Health
Research shows that sustaining adequate levels of selenium can help reduce risk for many chronic illnesses, including cardiovascular disease, thyroid diseases, certain cancers and possibly mitigate cognitive decline.
- Cognitive decline – our blood levels of selenium naturally decrease with age. Studies have been investigating various protective roles of selenium supplementation against age related cognitive decline. One randomized trial found that older adults, with average age of 77, who were experiencing mild cognitive impairment, benefitted from daily intake of Brazil nuts for selenium. This group had improvements in verbal fluency and constructional praxis (ability to link visual perception with motor skills) as compared to participants in the control group.4 More research is being done as, the results to date are inconclusive as to whether selenium supplementation can prevent Alzheimer’s disease in a healthy individual.5
- Thyroid diseases – selenium plays a vital role in thyroid hormone synthesis and metabolism. We store more selenium in the thyroid than in any other gland in the body and studies show supplements may be helpful in improving quality of life for persons with Graves’ disease, an autoimmune disorder that causes hyperthyroidism, or overactive thyroid.6
- Cardiovascular disease – selenium’s antioxidant capabilities can reduce oxidation of lipids in our blood vessels, decreasing inflammation and the clumping of platelets which can lead to heart disease.7 25 observational studies have shown that persons with the lowest levels of selenium may have highest risk of hypertension or heart disease, although levels that are excessive may increase risk in certain persons.8,9 A review of studies with about 44,000 participants found that supplementing selenium reduced inflammatory markers of heart disease, like C-reactive protein (CRP), and boosted protective compounds, like glutathione peroxidase (GSH-Px), an antioxidant enzyme that can convert harmful chemical structures into safe, healthy compounds.10
- Cancer – selenium’s ability to support DNA repair and its role in supporting the immune system have led to much study in how this nutrient could impact cancer risk. Numerous studies and review papers suggest that persons with adequate selenium levels, compared with those who are deficient, have reduced risk up to 30% for cancers like colorectal, prostate, lung, stomach and skin. While randomized supplement trials for prevention have not yielded consistent results, the FDA approved a qualified health claim in 2003 for foods and supplements containing selenium.2,11
Risks of Inadequate Selenium
Selenium deficiency can have widespread detrimental effects on the cardiovascular system. Studies have found an increased risk for cardiovascular diseases like hypertension, Keshan’s and heart attack, because selenium helps protect the heart from certain toxins and viral infections.12 Risks of deficiency also include male infertility and osteoarthritis.
Food sources of Selenium
Brazil nuts and seafood are excellent sources of selenium in the diet. Selenium is also found in foods like breads, grains, meat, poultry and eggs.4 Soil’s pH and its richness in selenium dictates how much of this nutrient is in each food, especially plant foods. When soil is depleted of selenium, less is available in the foods we eat.2,3 Adults require at least 55 mcg of selenium per day to maintain health, while amounts more than 400 mcg may elicit toxicities.13
- Sunde RA. Selenium. In: Ross AC, Caballero B, Cousins RJ, Tucker KL, Ziegler TR, eds. Modern Nutrition in Health and Disease. 11th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2012:225-37
- Loef M, Schrauzer GN, Walach H. Selenium and Alzheimer’s disease: a systematic review. J Alzheimers Dis 2011;26:81-104
- Marcocci C, Kahaly GJ, Krassas GE, Bartalena L, Prummel M, Stahl M, et al. Selenium and the course of mild Graves’ orbitopathy. N Engl J Med 2011;364:1920-31
- Rayman MP. Selenium and human health. Lancet 2012;379:1256-68
- Flores-Mateo G, Navas-Acien A, Pastor-Barriuso R, Guallar E. Selenium and coronary heart disease: a meta-analysis. Am J Clin Nutr 2006;84:762-73.
- Bleys J, Navas-Acien A, Guallar E. Serum selenium levels and all-cause, cancer, and cardiovascular mortality among US adults. Arch Intern Med 2008;168:404-10.
- Dennert G, Zwahlen M, Brinkman M, Vinceti M, Zeegers MP, Horneber M. Selenium for preventing cancer. Cochrane Database Syst Rev 2011:CD005195.
- Chun OK, Floegel A, Chung SJ, Chung CE, Song WO, Koo SI. Estimation of antioxidant intakes from diet and supplements in U.S. adults. J Nutr 2010;140:317-24.
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