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Advanced Health and Life Extension |
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Selenium Trace Element NutritionWhat is selenium?Selenium is an essential trace mineral that is essential for life. It is also a toxic metal when consumed in excess. Selenium is required to activate various key enzymes, including the antioxidant glutathione peroxidase, the metabolic enzyme thioredoxin reductase, and the thyroid-hormone-activating enzyme iodothyronine deiodinase. Food sources of selenium include brazil nuts, yeast, whole grains and seafood. Selenium content of food is dependent on selenium content in the soil and both are highly variable. Selenium: The Anticancer MineralEpidemological studies recognized a connection between cancer incidence and low levels of selenium in the blood as early as 1969. Researchers noted that breast cancer rates were low in areas where selenium levels in the soil and food were high and high in areas where selenium levels were low. The same correlation was found between death rates and selenium levels. Similar correlations were subsequently found in animal studies. In humans, it has been observed that a 200 mcg daily supplement given for four years led to a significant reduction in cancer deaths and reduction in the incidence of prostate, lung, colorectal and some types of skin cancer. The control group received 85 mcg per day in their diet. It has also been observed that the known selenoenzymes are saturated with 90 mcg daily of selenium. This indicates that an additional anticancer mechanism is in play in addition to the antioxidant activity of selenium. A 2011 meta-analysis of nine randomized controlled clinical trials including 152,538 participants established that selenium supplementation cut risk for all cancers by 24%. The cancer-preventive effect rose to 36% in people with low baseline selenium levels. Selenium and Heart DiseaseEpidemiological data suggests an association between lower antioxidant intake and a greater incidence of heart disease. Evidence also suggests that oxidative stress from free radicals may promote heart disease. It is the oxidized form of low-density lipoproteins (LDL) that promotes plaque build-up in coronary arteries. Selenium is one of a group of antioxidants that may help limit the oxidation of LDL cholesterol and thereby help to prevent coronary artery disease. Selenium and ArthritisEpidemiological data indicates that individuals with rheumatoid arthritis have reduced selenium levels in their blood. The body's immune system naturally makes free radicals that can help destroy invading organisms and damaged tissue, but that can also harm healthy tissue. Selenium, as an antioxidant, may help to relieve symptoms of arthritis by controlling levels of free radicals. Recommended Daily Intake of Selenium:The Institute of Medicine has established a Recommended Dietary Intake for selenium. The RDA is the average daily intake that the Institutes of Medicine believe is sufficient for the nutrition needs of approximately 97% of the population.
The Institute of Medicine has also established upper tolerable intake levels for selenium. Those levels are established for supplements that carry a risk of toxicity at high levels. While selenium toxicity is rare, there is a condition called selenosis that results from excessive levels of selenium in the blood. The established upper levels for selenium are:
Selenium Deficiency:People in areas where the soil is depleted of selenium may be at risk of selenium deficiency. Individuals with absorption issues and certain disease states like AIDS may be deficient in selenium as well. The consequences of selenium deficiency include hypothyroidism, a weakened immune system and heart disease. Selenium ToxicityResearchers observed that the most powerful selenium anticancer effects often occurred at doses not far below the potentially toxic doses. This led to the study of the biochemistry of selenium's anticancer action in more detail, in an attempt to surmount the potential toxicity problem. Researchers have noted that organic forms of selenium are toxic at levels in the vicinity of 3,500 micrograms (3.5 milligrams) daily while Inorganic forms of selenium may be toxic at 900 mcg per day. Researchers have also noted that the various peoples around the world routinely get 400 to 600 mcg selenium from their diet, and Greenlanders may ingest as much as 1,300 mcg daily, without apparent ill effects. It has been observed that selenium (as high selenium yeast) is safe at both 200 and 400 mcg/day levels, even when taken for years. Different Forms of SeleniumSelenium exists in multiple chemical compounds. Three forms are recognized as important for cancer prevention. They are sodium selenite, L-selenomethionine, and selenium-methyl L-selenocysteine. Inorganic sodium selenite is more effectively at increasing genetic expression of the main selenium-containing antioxidant enzyme glutathione peroxidase in healthy cells. Sodium selenite also has an anti-cancer mechanism. It selectively generates toxic reactive oxygen species and facilitates targeted destruction of mitochondria that exist in tumor cells but not in healthy tissue. In contrast, L-selenomethionine increases cancer cell death by apoptosis but only in cells with an intact "suicide" gene called p53. Selenium-methyl L-selenocysteine, on the other hand, induces apoptosis in mutated cancer cells that lack this vital control mechanism. Sodium selenite is more frequently metabolized to the toxic metabolite hydrogen selenide (H2Se). Hydrogen selenide does have anticancer effects but it is more toxic than L-selenomethionine. Its primary mode of killing cancer cells (and at high levels, normal cells) is through the process of cell necrosis. Cell necrosis provokes inflammation and may kill healthy cells along with cancer cells. Some studies suggest that the dosage of sodium selenide that is necessary for killing cancer cells approaches the dosage that proves toxic to healthy cells. Selenium-methyl L-selenocysteine is found naturally in some vegetables including garlic, brassicas, leeks, and onions, especially when these are grown in high selenium soil. Selenium-methyl L-selenocysteine is easily converted to methylselenol. Rather than killing cancer cells by necrosis, methylselenol kills cancer cells through apoptosis. Apoptosis is an orderly process of cellular self-destruction that does not provoke inflammatory responses. Methylselenol is also known to inhibit angiogenesis in beginning cancer tumors. Angiogenesis, the creation of new blood vessels, is necessary for cancer cells to grow into a tumor. Selenium-methyl L-selenocysteine does not accumulate in the body and is considered to be non-toxic. Selenium DosageThe RDA (Recommended Dietary Allowance) has been set at 55 mcg. of selenium for an adult. This is the intake level required to avoid manifesting obvious defeciency disorders and symptoms. The selenoenzymes have optimum levels when the selenium intake is around 90 mcg per day. For cancer prevention, doses of 200 to 400 mcg of methylselenocysteine are generally considered safe without medical supervision. Nutritionally-oriented physicians may use as much as 900 to 2,000 mcg selenium from Selenium-methyl L-selenocysteine daily as part of a comprehensive cancer treatment protocol. Selenium Drug InteractionsCertain medications may interact with Selenium. Consult with your physician and pharmacist if taking medication and before taking more than an RDA dosage of selenium. Look up your medications in the Physician's Desk Reference and check for interactions listed there. Selenium SupplementsHere are some recommended Selenium Supplements. Super Selenium Complex This supplement contains a balanced blend of all three selenium compounds mentioned above. Selenium Related Articles in Life Extension MagazineWhat Forms Of Selenium Protect Against Cancer?, Scientifically reviewed by: Dr. Amanda Martin, DC, in May 2022. Written by: Kirk Stokel. How To Obtain Optimal Benefits From Selenium, Scientifically reviewed by: Dr. Crystal M. Gossard, DCN, CNS, LDN, in May 2022. Written by: Alice Langstrom. CoQ10 And Selenium Reduce Cardiovascular Death, Scientifically reviewed by Dr. Gary Gonzalez, MD, in December 2021. Written by: Randy Whitmore. Selenium, Scientifically reviewed by: Dr. Gary Gonzalez, MD, in January 2021. Written by: Julius G. Goepp, MD. Selenium, Scientifically reviewed by: Dr. Gary Gonzalez, MD, in October 2022. Written by: Laurie Mathena. Selenium, Scientifically reviewed by: Dr. Gary Gonzalez, MD, in January 2021. Written by: Life Extension Editorial Staff. Selenium’s Impact on Cancer Reduction, Scientifically reviewed by: Dr. Amanda Martin, DC, in May 2022. Written by: Sarah Lewis. CoQ10 and Selenium Reduce Cardiovascular Risks, Scientifically reviewed by: Dr. Gary Gonzalez, MD, in May 2022. Written by: Justin Rogers. Getting Serious about Selenium, Scientifically reviewed by: Dr. Gary Gonzalez, MD, in January 2021. Written by: Life Extension Editorial Staff. In The News: Higher Selenium Levels Could Improve Breast Cancer Survival, Scientifically reviewed by: Dr Gary Gonzalez, MD, in July 2021. Written by: Life Extension Editorial Staff. CoQ10 and Selenium, Diabetes/cardiovascular disease Conferences, Tocotrienols, and blood sugar, Scientifically reviewed by Dr. Gary Gonzalez, MD, in May 2022. Written by: Life Extension Editorial Staff. Selenium Is Found to Reduce Cancer, Scientifically reviewed by: Dr. Gary Gonzalez, MD, in January 2021. Written by: Life Extension Editorial Staff. Selenium ReferencesClick to Expand ReferencesComb, G. Impact of selenium and cancer prevention findings on the nutrition-health paradigm. Nutr Cancer 2001, 40:6-11. Medina, D. et al. Se-methylselenocysteine: A new compound for chemoprevention of breast cancer. Nutr Cancer 2001, 40:12-17. Passwater, R. Selenium Against Cancer and AIDS. New Canaan CT: Keats, 1996:47-48. Passwater, R. Selenium as Food and Medicine. New Canaan CT: Keats, 1980:18. Duffield, A. et al. An estimation of selenium requirements for New Zealanders. Am J Clin Nutr 1999, 70:896-903. Clark, L. et al. Decreased incidence of prostate cancer with selenium supplementation: results of a double-blind cancer prevention trial. Br J Urol 1998, 81:730-34. Clark, L. et al. The nutritional prevention of cancer with selenium 1983-1993: a randomized clinical trial. JAMA 1996, 276:1957-63. Davis, C. et al. The chemical form of selenium influences 3,2'-dimethyl-4-aminobiphenyl-DNA adduct formation in rat colon. J Nutr 1999, 129:63-69. lp C. and Hayes, C. Tissue selenium levels in selenium-supplemented rats and their relevance in mammary cancer prevention. Carcinogenesis 1989, 10:921-25. lp C. Lessons from basic research in selenium and cancer prevention. J Nutr 1998, 128:1845-54. Lu, J. and Jiang, C. Antiangiogenic activity of selenium in cancer chemoprevention: metabolite-specific effects. Nutr Cancer 2001, 40:64-73. Hetts, S. To die or not to die: an overview of apoptosis and its role in disease. JAMA 1998, 279:300-07. Whanger, P. Selenocompounds in plants and animals and their biological significance. J Am Coll Nutr 2002, 21:223-32. Ip, C. and Lisk, D. Characterization of selenium provirtuals and anticarcinogenic responses in rats fed natural sources of selenium-rich products. Carcinogenesis 1994, 15:573-76. Ip, C. et al. In vitro and in vivo studies of methylseleninic acid: evidence that a monomethylated selenium metabolite is critical for cancer chemoprevention. Cancer Res 2000, 60:2882-86. Yoshida M, Fukunaga K, Tsuchita H, Yasumoto K. An evaluation of the bioavailability of selenium in high-selenium yeast. J Nutr Sci Vitaminol 1999;45:119-28. Dworkin BM. Selenium deficiency in HIV infection and the acquired immunodeficiency syndrome (AIDS). Chem Biol Iteract 1994;91:181-6. Moore JA, Noiva R, Wells IC. Selenium concentrations in plasma of patients with arteriographically defined coronary atherosclerosis. Clin Chem 1984;30:1171-3. Knekt P, Heliovaara M, Aho K, et al. Serum selenium, serum alpha-tocopherol, and the risk of rheumatoid arthritis. Epidemiology 2000;11:402-5. Yang GQ, Zhou RH. Further observations on the human maximum safe dietary selenium intake in a seleniferous area of China. J Trace Elem Electrolytes Hlth Dis 1994;8:159-65. Contempre B, Dumont JE, Ngo B, et al. Effects of selenium supplementation in hypothyroid subjects of an iodine and selenium deficient area: The possible danger of indiscriminate supplementation of iodine deficient subjects with selenium. J Clin Endocrinol Metabol 1991;73:213-5. Duffield-Lillico AJ, Slate EH, Reid ME, et al. Selenium supplementation and secondary prevention of nonmelanoma skin cancer in a randomized trial. J Natl Cancer Inst 2003;95:1477-81. Panel on Dietary Antioxidants and Related Compounds, Food and Nutrition Board, Institute of Medicine, National Academy of Sciences. Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium, and Carotenoids. National Academy Press, Washington, D.C., 2000. Institute of Medicine, Food and Nutrition Board. Dietary Reference Intakes: Vitamin C, Vitamin E, Selenium, and Carotenoids. National Academy Press, Washington, DC, 2000.
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