Selenium from selenium-enriched yeast supplements is more bioavailable than selenium from an inorganic source such as sodium selenite. Selenium from selenium-enriched yeast supplements also tends to be less toxic. These are the conclusions from a 2008 evaluation undertaken by a European Food Safety Authority (EFSA) scientific panel [EFSA 2008].
To quote directly from the report:
“Despite the higher bioavailability of selenium from organic sources such as selenium-enriched yeast, the toxicity of these organic forms has been shown in a number of studies in experimental animals to be lower than that of inorganic selenite or selenate.”
Study data indicate that organic selenium is more bioavailable than inorganic selenium. Studies in which different selenium preparations have been compared head-to-head point towards a higher bioavailability of selenium from yeast than from inorganic sources [Hadrup & Ravn-Haren 2021].
Selenium Species in Selenium-Enriched Yeast
The major selenium constituent in selenium-enriched yeast supplements is selenomethionine. Typically, selenomethionine accounts for approximately 60 – 85% of the total selenium in the selenium-enriched supplements [EFSA 2008]. The amount of selenomethionine varies according to the manufacturer’s production methods.
In contrast to pure selenomethionine and inorganic selenium supplements, selenium-enriched yeast supplements contain a range of minor organic selenium species. In qualitative analyses of selenium-enriched products, researchers have identified more than 30 organic selenium species. Typically, the selenium-enriched supplements contain no more than one percent inorganic selenite [Larsen 2004].
Richie et al have demonstrated the importance of having selenium species other than selenomethionine available in selenium-enriched yeast supplements. Their clinical trial showed reductions in biomarkers of oxidative stress in healthy men following supplementation with selenium-enriched yeast but not following supplementation with pure selenomethionine. Logically, the selenium-containing compounds other than selenomethionine must account for the decrease in oxidative stress [Richie 2014].
Equally thought-provoking is the fact that supplementation with pure selenomethionine in the SELECT Trial did not reduce the risk of prostate cancer. In the Nutritional Prevention of Cancer Trial, on the other hand, supplementation with a selenium-enriched yeast preparation was significantly associated with a reduction in prostate cancer risk [Schrauzer 2009].
Selenium Intakes and Status in Europe
The EFSA panel estimated the dietary intake of selenium by the European population to be in the range of 27-70 mcg/day. Finland, which adds selenium to agricultural fertilizer, has higher intakes. Thus, daily consumption of a nutritional supplement containing 100 mcg of selenium should result in a total daily selenium intake of 130-170 mcg/day [EFSA 2008].
In a 2024 study, Larsen et al noted that a healthy adult’s serum selenium status needs to be in the range 120-130 mcg/L. This is the serum selenium concentration required to optimize the circulating concentration of selenoprotein P, the primary transporter of selenium in the blood. To achieve this selenium status, Larsen et al estimated that the required selenium intake is at least 100 mcg per day [Larsen 2024].
In selenium supplementation, the organic compounds are more easily absorbed by human organisms than the inorganic compounds are [Kieliszek 2019].
Tolerable Upper Intake Level for Selenium
In 2023, an EFSA scientific panel established an upper limit of 255 mcg of selenium per day for adult men and women (including pregnant and lactating women).
Safety of Selenium-Enriched Yeast Supplements
Both organic and inorganic forms of selenium can have a toxic effect on the human organism. The toxicity of selenium depends on the dose [Kieliszek 2019]. The EFSA panel reported that the highest long-term daily intake that can be ingested without the development of toxicity is approximately 800 mcg. Prolonged daily intakes of selenium doses of 1000 mcg or greater may cause adverse reactions [EFSA 2008].
Clinical studies conducted with selenium-enriched yeast show no evidence of toxicity at selenium intakes up to 340 mcg/day and at whole-blood levels of 440 selenium mcg/L for a period of over 4 years [EFSA 2008].
The EFSA scientific panel concluded that selenium-enriched yeast as a source of selenium when used in foods (including food supplements) for the general population does not present a safety concern at the proposed intake levels, i.e., at 50, 100, or 200 mcg [EFSA 2008].
The scientific panel reported that supplement-induced increases in plasma selenium concentrations result in a new steady-state serum level. The new steady-state level is maintained unchanged for many years if the level of selenium intake is unchanged [EFSA 2008].
Once absorbed, the selenomethionine in selenium-enriched yeast supplements will be diverted into pathways of methionine metabolism or will be metabolized to other functional forms of selenium (e.g., selenocysteine). It will be stored as selenoproteins.
The half-life of selenomethionine is 252 days. This is longer than the half-life of inorganic selenite (102 days). The absorbed selenomethionine gets incorporated into a long-term body pool. Typically, the steady-state of selenium from selenium-enriched yeast supplements is achieved after 6-12 months of supplementation. The selenium is incorporated into tissue proteins in the plasma albumin, the skeletal muscle, the liver, and the red blood cells. It can be released later, as necessary, to maintain increased serum selenium status. In this way, selenomethionine seems to be extensively utilized and re-utilized [EFSA 2008].
No Worries About the Yeast in Selenium-Enriched Yeast
Selenium-enriched yeast supplements are produced in fermentation process. Manufacturers feed inorganic selenium to live yeast cells. The yeast cells incorporate the selenium into the yeast cell walls. The selenium becomes a constituent part of the proteins in the yeast cells. The inorganic selenium is converted natural organic selenium in the yeast cells. The next step in the process is to pasteurize the selenium-enriched yeast, thus causing the yeast cells to die.
Even if there should be residual live yeast in the supplement (unlikely), the EFSA panel makes the following points [EFSA 2008]:
- the quantity of yeast ingested as a result of the use of supplements containing selenium-enriched yeast would be small
- the cellular constituents of the yeast would be endogenous in the human body
- the quantity of yeast ingested would be unlikely to present an allergenic risk
Conclusion: Selenium-Enriched Yeast Supplements
There is higher bioavailability of selenium from organic sources such as selenium-enriched yeast.
The toxicity of these organic forms is lower than the toxicity of inorganic selenite or selenate.
The yeast cells in selenium-enriched yeast supplements are dead cells – they are harmless.
Sources
EFSA Panel on Nutrition, Novel Foods and Food Allergens (NDA). Scientific opinion on the tolerable upper intake level for selenium. EFSA Journal. 2023 Jan 20;21(1):e07704.
EFSA. Selenium‐enriched yeast as source for selenium added for nutritional purposes in foods for particular nutritional uses and foods (including food supplements) for the general population ‐ Scientific Opinion of the Panel on Food Additives, Flavourings, Processing Aids and Materials in Contact with Food. EFSA Journal. 2008;766:1-42.
Hadrup N, Ravn-Haren G. Absorption, distribution, metabolism and excretion (ADME) of oral selenium from organic and inorganic sources: A review. J Trace Elem Med Biol. 2021 Sep;67:126801.
Kieliszek M. Selenium: Fascinating microelement, properties and sources in food. Molecules. 2019 Apr 3;24(7):1298.
Larsen EH, Hansen M, Paulin H, Moesgaard S, Reid M, Rayman M. Speciation and bioavailability of selenium in yeast-based intervention agents used in cancer chemoprevention studies. J AOAC Int. 2004 Jan-Feb;87(1):225-32.
Larsen C, Winther KH, Cramon PK, Rasmussen ÅK, Feldt-Rasmusssen U, Knudsen NJ, Bjorner JB, Schomburg L, Demircan K, Chillon TS, Gram J, Hansen SG, Brandt F, Nygaard B, Watt T, Hegedus L, Bonnema SJ. Selenium supplementation and placebo are equally effective in improving quality of life in patients with hypothyroidism. Eur Thyroid J. 2024 Jan 1;13(1):e230175.
Richie JP Jr, Das A, Calcagnotto AM, Sinha R, Neidig W, Liao J, Lengerich EJ, Berg A, Hartman TJ, Ciccarella A, Baker A, Kaag MG, Goodin S, DiPaola RS, El-Bayoumy K. 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.
Schrauzer GN. Selenium and selenium-antagonistic elements in nutritional cancer prevention. Critical Reviews In Biotechnology. 2009;29(1):10-17.
The information presented in this review article is not intended as medical advice. It should not be used as such.