Properties of a high-selenium yeast preparation

The element selenium is seldom found alone and unbound. In the body, it forms a part of the amino acids selenomethionine and selenocysteine and functions as a component of some 25 selenoproteins. The high-selenium yeast used in nutritional supplements is produced by enriching Saccharomyces cerevisiae yeast (also known as baker’s yeast or brewer’s yeast) with selenium. As the yeast grows, it absorbs the selenium. The result is an organic high-selenium yeast that has a relatively good absorption and bio-availability. It provides several species of selenium that are necessary for many cellular functions in the body. The yeast in the high-selenium yeast tablets is dead. It cannot cause yeast infections.

The evidence from clinical studies shows that high-selenium yeast preparations give the best health outcomes [Alehagen; Blot; Clark; Yu].

Today, I want to look at the documented properties of the high-selenium yeast preparation that was developed for use in the PRECISE studies.  PRECISE is the acronym for PREvention of Cancer by Intervention with SElenium.  The PRECISE studies were designed to test the effectiveness of selenium supplementation at preventing cancer.

The preparation is also the high-selenium yeast preparation used in the KiSel-10 study of combined selenium and Coenzyme Q10 supplementation of healthy elderly citizens to protect against heart disease.  Professor Urban Alehagen and the researchers at Linköping University in Sweden have written about the special interrelationship between selenium and Coenzyme Q10: our cells need adequate selenium status to obtain optimal concentrations of Coenzyme Q10, and our cells need adequate Coenzyme Q10 status to realize optimal selenoprotein function [Alehagen].

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Serum/plasma selenium status and protection against cancer

In cancer prevention, there seems to be a U-shaped response to selenium supplementation. The threat of adversity is greater at the lower and higher levels of serum/plasma selenium. For example, Emily Chiang and her colleagues posit that the optimal serum selenium level for the reduction of prostate cancer risk is between 119 and 137 micrograms per liter. (Graph for illustration purposes only)

The documentation in various systematic reviews and meta-analyses of selenium and cancer studies shows a significant inverse association between selenium intake and/or plasma/serum selenium status and cancer [Lee; Hurst; Cai].

There is some evidence of a U-shaped relationship between plasma/serum selenium status and protection against cancer [Hurst; Rayman].  Low plasma/serum selenium status clearly correlates with higher risk of cancer.  High plasma/serum selenium status correlates with no increased protective effect against cancer.  The key is to find the supplement doses and subsequent plasma/serum status that give the best protection in between the two extremes.

Evaluating the evidence from published studies is complicated.  We need to remember that the following factors affect the relationship between selenium status and/or intake and cancer risk:

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Selenium and antioxidants in combination against cancer

Nothing is clear-cut, it seems.  Yes, we want to eat fruits and berries for their antioxidant content.  But, fruits and berries are full of the sugar called fructose.  So, like everything else, we need to eat fruits and berries in moderation.  In this report, I focus on studies of selenium and antioxidant combinations to prevent cancer.

On the topic of cancer and selenium as a cancer chemo-preventive agent, we know some basic facts from published research:

  • selenium prevents or delays tumor development in animals [Schrauzer]
  • regions with low selenium intakes are regions with higher incidence of cancer [Schrauzer]
  • greater exposure to selenium is associated with lower incidence of cancer [Cai]
  • single interventions with high-selenium yeast preparations reduce the incidence of cancer [Clark; Yu; Li]

What do randomized controlled studies reveal about the efficacy of selenium and antioxidant combinations against the development of cancerous tumors, I wondered.

The first studies to come to mind were the Linxian Nutritional Intervention Studies, which are probably just as important in the history of selenium and cancer research as Professor Larry Clark’s Nutritional Prevention of Cancer study is.

Professor Blot’s Linxian Nutrition Intervention Studies in China

The Linxian studies were a very big research undertaking.  The researchers enrolled 29,584 study participants aged 40 to 69 years from four Linxian County municipalities.  The study participants lived in a region of China characterized by constantly low intakes of selenium and by high cancer mortality rates.

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Selenium as a single intervention for cancer prevention

In many regions of the world, low soil selenium levels result in the production of low-selenium wheat.  Then, the milling and processing of the wheat results in 14% less selenium in wheat flour than is found in the raw wheat.  The combined result is decreased intakes of dietary selenium and increased risk of cancer. Studies show that supplementation with high-selenium yeast preparations in low-selenium regions has a cancer preventive effect.

On this blog site,, we focus on the health and nutritional benefits of selenium supplementation.  We look at the following types of studies:

  • human studies more so than lab studies or animal studies
  • intervention studies more so than observational studies
  • randomized controlled studies whenever possible

Cancer and Selenium as a single intervention agent

The best studies of selenium as a single intervention to prevent or treat cancer show significant results in regions with low selenium intakes and/or high cancer risk.

Professor Clark’s NPC study

The big breakthrough came when Professor Larry Clark published the results of the Nutritional Prevention of Cancer (NPC) study in the prestigious journal JAMA: The Journal of the American Medical Association.

The NPC study was a multi-center randomized, double-blind, placebo-controlled study carried out in a selenium-poor region of the southeastern United States.  The study participants who took 200 micrograms of a high selenium yeast preparation over an average 4.5-year period showed significant health benefits (as compared to placebo):

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Selenium and liver cancer: the Qidong study results

China is a country with many selenium-poor regions. The people living in these regions have paid the price with high rates of heart disease, bone disease, and various forms of cancer. Selenium supplementation has proven beneficial in China.

Some 50 years ago now, Chinese researchers began to understand the health risks associated with low selenium status.  Cross-sectional studies showed an association between low selenium concentrations in cereal grains, the low selenium status of local citizens, and the incidence of Keshan disease, a heart disease with high death rates.  The administration of selenium supplements in intervention studies resulted in significant reductions in the incidence of Keshan disease [Chen 2012].  Selenium status is one of the main factors contributing to the development of Keshan disease.

Selenium and Kashin-Beck disease
Not long afterwards, Chinese researchers realized that Kashin-Beck disease, a disease of the bone, is prevalent in regions of China and Tibet that are poor in selenium.  The researchers saw that a deficiency of selenium and iodine was a common factor Kashin-Beck disease regions [Yao 2011].

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Selenium and cancer prevention: The Linxian Study

In the 1990s and before, the diets of the people in the Linxian province in China were poor in important micronutrients. Selenium status among the residents was notably low. Cancer rates were high. Supplementation with selenium and other antioxidants reduced cancer incidence and mortality.

The Nutrition Intervention Trials conducted in the Linxian province in China yielded some of the first promising results linking selenium supplementation to the reduction of cancer incidence and mortality.  The Linxian province at the time was characterized by a selenium-poor diet.

The treatment group that received selenium supplements was the group that showed significant health benefits of the supplementation:

  • Significantly lower total mortality
  • Significantly lower cancer mortality
  • Significantly lower stomach cancer mortality

The reduced mortality rates began to become apparent already after 1 – 2 years of supplementation.  The patterns for reductions in cancer incidence generally approximated the patterns for cancer mortality [Blot].

The Linxian study results were exciting because they were published in the Journal of the National Cancer Institute and because they appeared before the results of the Nutritional Prevention of Cancer study in the United States [Clark].

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We must not waste selenium

Selenium exists only in scarce quantities. Adequate dietary and supplemental intakes are vital for human health.  We need to use it carefully, and we need to begin to stockpile it for the use of future generations.

Selenium is a trace element.  It exists only in rare quantities in the world.  It is produced primarily as a by-product of the process of mining copper.  It is not recyclable.  It is very unevenly distributed in the soils of the earth.

Consequently, the availability of selenium in grasses and grains and, at the next stage of the food chain, in animals, varies considerably from region to region in the world. The human dietary intakes of selenium vary accordingly around the world.

Selenium a vital nutrient for humans
Selenium is a necessary micronutrient that our bodies do not produce.  We get our selenium primarily from our diets.  Selenium is important for good immune system function, good thyroid function, good reproductive function, and good protection of our cells’ DNA.

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Selenium supplements and breast cancer

Studies show that selenium intake and status are associated with breast cancer risk.  Low selenium status indicates an increased risk of breast cancer.

In many countries, breast cancer is the most commonly diagnosed and treated form of cancer.  A 2014 meta-analysis of 16 studies has shown that there is a statistically significant association between serum selenium status and risk of breast cancer.  The lower the serum selenium concentration, the greater the risk of breast cancer [Babaknejad].

What do we know about selenium and breast cancer?
Breast cancer is a frustrating topic for the selenium researcher.  There is not enough evidence to permit definitive statements about the effects of selenium supplementation on the prevention of breast cancer.

For example, the Nutritional Prevention of Cancer (NPC) study – a study that showed significant associations between selenium supplementation and reduced risk of colorectal, lung, prostate, and total cancer – did not enroll enough women for the effect of selenium supplementation on breast cancer to be studied [Clark].

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How much selenium every day?

Yes, good health depends on good genes. But it also depends on good diet, good exercise, good sleep, and adequate intakes of essential bio-nutrients such as selenium and Coenzyme Q10.

The proper daily dosage of selenium for normal people?   Normal people?  How many of us are approximately normal?  68 percent of us, perhaps?  Yes, we humans are more the same in many ways than we are different.  However, there is considerable biochemical variation amongst us humans.  So, it is difficult to say who is average and normal and then suggest an ideal daily dosage of selenium.

What do the numbers from selenium studies say?
Let’s look at the numbers from published research and see what sense we can make of them.  Remember: we humans need adequate plasma selenium concentrations for optimal antioxidant and anti-viral and anti-carcinogenic protection [Schrauzer 2009].

Putative beneficial range for plasma selenium status
Hurst and Fairweather-Tait et al, researchers based at Norwich Medical School, University of East Anglia, in the United Kingdom have suggested that the “putative beneficial range” lies between 120 and 150 nanograms of selenium per milliliter of plasma [Hurst 2010].

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Selenium and the prostate

Next to skin cancer, prostate cancer is the most common cancer in men in the United States. It is a leading causes of cancer death among men of all races and ethnic backgrounds. Low selenium status is associated with increased risk of prostate cancer.

There have been some recent research results relating to selenium supplementation and prostate gland tissue.  Researchers in The Netherlands have published results showing that a five-week daily intervention with a high-selenium yeast supplement, 300 micrograms daily, is associated with a down-regulation of genes that are involved with cellular growth and proliferation, with cellular immune response, and with inflammation processes.  Also down-regulated by the selenium supplementation is the activity of genes involved with wound-healing [Kok 2017].

The Dutch study was a randomized, double-blinded, placebo-controlled study.  Interestingly, the researchers saw the opposite effect in the placebo group.  In the placebo group, there was an up-regulation of the genes involved in cellular immune response [Kok 2017].

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