A Quick Guide to Selenium

A Quick Guide to Selenium

What Is Selenium? 

Selenium is a trace element that is naturally present in many foods, and also available as a dietary supplement. It is necessary for the functioning of the endocrine, immune, and cardiovascular systems. Selenium is a component of more than two dozen selenium proteins that play critical roles in reproduction, thyroid hormone metabolism, DNA synthesis, and protection from oxidative damage and infection. Selenium deficiency may cause a range of symptoms including infertility in men and women, muscle weakness, fatigue, mental fog, hair loss, and a weakened immune system. (1)

The availability of selenium for the body varies greatly around the world depending on the selenium content of the soil and the accumulation of selenium in farm crops and animals along with the intake of additional selenium through dietary supplements.

The recommended amounts for adequate selenium intake for adults range from 25 to 100 micrograms (μg) per day. Dietary supplements containing selenium up to 200 μg/day are considered safe, inexpensive, and widely available. Higher levels of selenium may help support the immune systems of people with HIV, influenza, tuberculosis, and hepatitis. (2) 

Measurement of selenium levels in the body is done using plasma, serum, and urine. Analyses of hair or nail selenium can be used to monitor longer-term intakes over months or years. Plasma or serum concentrations of 8 μg/dl or higher of selenium in healthy people normally meet the body’s needs. (3)

Selenium And The Immune System 

Selenium is considered an antioxidant and thus is crucial for the health and proper functioning of the immune system. Free radicals are a byproduct of the body’s metabolism, and when they overwhelm the body's ability to regulate them, a condition known as oxidative stress results. A balance between free radicals and antioxidants is necessary for proper physiological function. By lowering oxidative stress, selenium can help strengthen the immune system, reduce inflammation, defend against chronic conditions, reduce DNA damage, and destroy malignant cells. (1)

Heart Health And Selenium

A diet rich in selenium may help support heart health by reducing inflammation and oxidative stress in the body. Oxidative stress and inflammation have been linked to atherosclerosis, the buildup of plaque in arteries. Atherosclerosis can lead to dangerous health problems like strokes, heart attacks, and other heart conditions. (4)

An interesting study was performed in Iran on 100 patients undergoing open-heart surgery to measure the trend of selenium and its relationship with the patients’ outcomes after their open-heart surgery.   Based on previous studies, the impact of oxidative stress on the occurrence of multiple organ dysfunctions after surgery has been confirmed and remains a challenging unsolved problem. In past experimental studies, selenium supplementation appeared to affect the oxidative process and decrease postoperative complications after cardiac surgery.

Based on this study's results, selenium levels can affect patients' outcomes after open-heart surgery influencing the duration of hospitalization, surgery success, and rate of recovery. Therefore, serum selenium levels should be routinely measured before cardiac surgery and selenium supplements prescribed if needed. (5)

Selenium And Mental Health 

Alzheimer’s, a devastating condition that negatively affects thinking and behavior, is the sixth-leading cause of death in the United States. Since selenium concentrations decline with age, marginal or deficient concentrations may be associated with age-related declines in brain function. This is possibly due to decreases in selenium’s antioxidant activity. (6)

Several studies have shown that patients with Alzheimer’s have lower blood levels of selenium. A diet rich in selenium may help prevent mental decline and improve memory loss in people with Alzheimer’s. The Mediterranean Diet which is rich in high-selenium foods like seafood and Brazil nuts has been associated with a lower risk of developing Alzheimer’s. (7)

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Thyroid Health And Selenium 

The thyroid gland has the highest concentration of selenium per weight of any other organ tissue. And like iodine, selenium has important functions in thyroid hormone synthesis and metabolism. It protects the thyroid gland from oxidative stress and thus may help people with Hashimoto’s illness and other types of thyroid disorders.

The thyroid gland also affects mental health. Margaret Rayman, PhD., reports that selenium deprivation leads to depressed mood and that high dietary or supplementary selenium seems to improve mood. She also states that selenium intake might affect thyroid hormone metabolism and thus should affect mood and cognitive functions. (8)

Selenium deficiency is a problem in some countries, especially China. A study of over 6,000 people found that low serum levels of selenium were associated with an increased risk of autoimmune thyroiditis and hypothyroidism. Subsequently, consumption of meat and high selenium green tea seemed to significantly protect the participants from hypothyroidism. (9)

The Relationship Between Selenium And Asthma 

Asthma has been associated with increased levels of oxidative stress and inflammation in the body. Selenium’s ability to reduce inflammation suggests that it may help reduce asthma-related symptoms. Research has also found that people who have asthma have lower blood levels of selenium. One study found that giving people with asthma 200 μg of selenium per day reduced their use of corticosteroid medications. (10)

Malignancies And Selenium 

Regarding the question of selenium and malignancies, a review of 69 studies that included over 350,000 people found that having a high blood level of selenium obtained through foods, not supplements, was associated with a lower risk of certain types of malignancies. High selenium exposure appeared to have a protective effect on the risk of abnormal cell growth. There is also some evidence that selenium may affect progression and metastasis. More research needs to be done in this area. (11)

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Selenium And A Healthy Diet 

The Mediterranean Diet, which includes Extra Virgin Olive oil, seafood, legumes, nuts, seeds, leafy greens, and fruits, seems to be most supportive for those concerned with selenium balance. But it’s important to remember that the amount of selenium in plant-based foods varies depending on the selenium content of the soil in which they are grown.

The following foods are great sources of selenium:

  • Oysters
  • Brazil nuts and walnuts
  • Yellowfin tuna, cod, red snapper, herring, sardines
  • Eggs
  • Sunflower seeds
  • Shiitake mushrooms
  • Beef and poultry, kidney and other organs
  • Tomatoes, garlic, onions, celery, broccoli, spinach
  • Cereals, grains, lima, or pinto beans (1, 12)

Being mindful of one’s selenium intake may be an important way to support overall good health, so be sure to add quality sources of nutrition into each day’s meals.

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Sources

  1.       Sunde RA., et al, Modern Nutrition in Health and Disease. 11th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2012:225-37.
  2.       Advanced Nutrition, 2015 Jan; 6(1): 73–82. DOI: 10.3945/an.114.007575
  3.       Sunde RA., et al. Encyclopedia of Dietary Supplements. 2nd ed. London and New York: Informa Healthcare; 2010:711-8
  4.       J Trace Elem Med Biol. 2017 Dec;44:8-16. DOI: 10.1016/j.jtemb.2017.04.009
  5.       Gohar Eslami, et al; Relationship Between Selenium Trace and Patient Outcome After Open-Heart Surgery. DOI: 10.5812/aapm.105895
  6.       Akbaraly TN, et al. Plasma selenium over time and cognitive decline in the elderly. Epidemiology 2007;18:52-8.
  7.       Am J Clin Nutr 2011 Sep, 94(3):892-9. DOI: 10.3945/ajcn.110.007815.
  8.       Margaret P. Rayman, Ph.D., The importance of selenium to human health. July 15, 2000, Lancet. 2000; 356: 233-241 https://doi.org/10.1016/S0140-6736(00)02490-9
  9.       The Journal of Clinical Endocrinology & Metabolism, Volume 100, Issue 11, 1 November 2015, Pages 4037–4047, https://doi.org/10.1210/jc.2015-2222
  10.   Bratisl Lek Listy, 2002;103(1):22-5. https://pubmed.ncbi.nlm.nih.gov/12061082/
  11.   Cai, X., Wang, C., Yu, W. et al. Selenium Exposure and Cancer Risk: An Updated Meta-analysis and Meta-regression. Sci Rep 6, 19213 (2016). https://doi.org/10.1038/srep19213
  12.   U.S. Department of Agriculture, Agricultural Research Service. Food Data Central, 2019. fdc.nal.usda.gov.

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