The trace mineral selenium functions primarily as a component of the antioxidant enzyme glutathione peroxidase. This valuable enzyme works with vitamin E and plays a pivotal role in preventing free radical damage to cell membranes. Not surprisingly, low levels of selenium in the body have been linked to a higher risk for cancer, cardiovascular disease, inflammatory diseases, and other conditions associated with increased free radical damage including premature aging and cataract formation. Low selenium levels are also associated with low immune function.
Health Benefits of Selenium Supplementation:
Maintaining proper selenium levels appear to be important in protecting against many health conditions. Therefore, it is not surprising to see that selenium supplementation has been shown to exert a number of beneficial effects in double blind clinical trials, but not all selenium supplements appear to offer the same health benefits. Here is a brief summary of some of the results from some of the positive studies with selenium supplementation:
- Antioxidant effects. In a double blind, placebo-controlled trial, 69 healthy men were given a selenium from a selenium-rich yeast known as SelenoExcell (200 or 285 μg/day) or selenomethionine (200 μg/day) for 9 months. While blood selenium levels increased by 93%, 54%, and 86% in the selenomethionine and low- and high-dose SelenoExcell groups, respectively, only the men receiving the SelenoExcell demonstrated a decrease in oxidative stress. Levels of standard markers of oxidative damage, 8-OHdG and 8-iso-PGF2α, were decreased 34% and 28%, respectively, versus no change in the selenomethionine group.1
- Heart disease prevention. In one double blind study, 81 patients who had a heart attack were randomly assigned to receive 100 mcg of selenium (from selenium-rich yeast) or a placebo. After 6 months, there were 4 fatal heart attacks and 2 non-fatal heart attacks in the placebo group compared to no deaths and 1 non-fatal heart attack in the selenium group.2
- Immune function enhancement. In one clinical trial selenium supplementation (200 mcg/day) to individuals with normal selenium concentrations in their blood resulted in a 118% increase in the ability of white blood cells to kill tumor cells and 82.3% increase in the activity of a type of white blood cell known as a “natural killer cell.” These white blood cells are given this name because of their powerful ability to kill cancer cells and microorganisms.3
- Cancer prevention. In the Nutritional Prevention of Cancer (NPC) study, supplementation with SelenoExcell was associated with a 50% reduction in cancer mortality, including a 52% decrease in prostate cancer incidence. Studies with other forms or sources of selenium, in contrast, have failed to show this effect (discussed below).
A Closer Look at Selenium and Prostate Cancer:
The results from studies looking at selenium in prostate cancer prevention have brought conflicting results. These may be related to the form of selenium being used and the ability of selenium to be incorporated into prostate cells. In the Nutritional Prevention of Cancer (NPC) study, supplementation with SelenoExcell, a selenium-enriched yeast, was associated with a 52% decrease in prostate cancer incidence.5 In contrast, in the SELECT study, selenomethionine failed to show any protective effects alone or when combined with synthetic vitamin E.6 The difference in results may be entirely related to the form of selenium being used (see above in regards to antioxidant activity).
Another factor to explain differing results is the effect of selenium supplementation on the concentration of selenium within prostate tissue. Selenomethionine has been shown to have only a modest effect in increasing prostate tissue selenium levels.7 In contrast, results from a double-blind study in men with prostate cancer show SelenoExcell is significantly more effective in increasing selenium levels in prostate tissue.8 In the study, 53 men were randomized to receive placebo, 200 mcg of high SelenoExcell, or 400 mcg of SelenoExcell for 4-6 weeks prior to surgery to remove their prostate gland. Results showed a clear dose effect in increasing the selenium content in prostatic tissue and provided a greater degree of selenium incorporation in prostate tissue compared to published results with selenomethionine. Specifically, while selenomethionine (200 mcg per day) was shown to increase the prostate selenium levels by 22%, SelenoExcell produced a 34% increase at the 200 mcg/day dosage and a 92% increase at the 400 mcg per day dosage. It is thought that increased selenium uptake in the prostate after supplementation with SelenoExcell as compared to selenomethionine may be the key difference in results seen in the NPC and SELECT studies.
In addition to acting as an antioxidant, selenium-rich yeast may also offer protection against cancer by immune system effects, detoxification of antagonistic metals, inactivation of nuclear transcription factors that stimulate cancer growth, and a host of effects on DNA and cellular replication.
What is SelenoExcell?
SelenoExcell originates from a special strain of non-GMO baker’s yeast (Saccharomyces cerevisiae) to provide a true food form of selenium. The particular yeast strain used in SelenoExcell is able to accumulate and incorporate selenium into proteins that enhance the absorption and utilization of selenium as noted above. The yeast is inactivated (dead) and cannot reproduce in the human body. Only the nutritional benefits remain.
In light of the cumulative data on selenium supplementation, it is clearly apparent that high selenium content yeast in the form of SelenoExcell is the preferred form. In addition to selenomethionine, there are inorganic selenium salts like sodium selenite available in the marketplace. However, selenium salts are less effectively absorbed and are not as biologically active compared to organic forms of selenium, especially SelenoExcell.
Cautions and Warnings:
Do not take selenium at levels greater than 400 mcg daily. In some people, dosages of selenium as low as 900 mcg per day over many months or years may produce signs of selenium toxicity. Signs and symptoms related to chronic selenium toxicity include depression, nervousness, emotional instability, nausea and vomiting, a garlic odor of the breath and sweat, and, in extreme cases, loss of hair and fingernails.
- Richie JP Jr, Das A, Calcagnotto AM, et al. Comparative effects of two different forms of selenium on oxidative stress biomarkers in healthy men: a randomized clinical trial. Cancer Prev Res (Phila). 2014 Aug;7(8):796-804.
- Korpela H, Kumpulainen J, Jussila E, et al. Effect of selenium supplementation after acute myocardial infarction. Res Commun Chem Pathol Pharmacol. 1989 Aug;65(2):249-52.
- Kiremidjian-Schumacher L, Roy M, Wishe HI, et al. Supplementation with selenium and human immune cell functions. II. Effect on cytotoxic lymphocytes and natural killer cells. Biol Trace Elem Res 1994;41:115-127.
- Duffield-Lillico AJ, Reid ME, Baseline characteristics and the effect of selenium supplementation on cancer incidence in a randomized clinical trial: a summary report of the Nutritional Prevention of Cancer Trial. Cancer Epidemiol Biomarkers Prev. 2002 Jul;11(7):630-9.
- Duffield-Lillico AJ, Dalkin BL, Reid ME, et al. Selenium supplementation, baseline plasma selenium status and incidence of prostate cancer: an analysis of the complete treatment period of the Nutritional Prevention of Cancer Trial. BJU Int. 2003 May;91(7):608-12.
- Lippman SM, Klein EA, Goodman PJ, et al. Effect of selenium and vitamin E on risk of prostate cancer and other cancers: the Selenium and Vitamin E Cancer Prevention Trial (SELECT). JAMA. 2009 Jan 7;301(1):39-51.
- Sabichi AL, Lee JJ, Taylor RJ, et al. Selenium accumulation in prostate tissue during a randomized, controlled short-term trial of l-selenomethionine: a Southwest Oncology Group Study. Clin Cancer Res. 2006 Apr 1;12(7 Pt 1):2178-84.
- Algotar AM, Stratton MS, Xu MJ, et al. Dose-dependent effects of selenized yeast on total selenium levels in prostatic tissue of men with prostate cancer. Nutr Cancer. 2011;63(1):1-5.