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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Prostate cancer risk and selenium status

Selenium supplements in the form of organic high-selenium yeast tablets provide the best cancer chemo-protection. These supplements are made using the yeast species Saccharomyces cerevisiae in a selenium-enriched growth medium. The yeast cells that produce the high selenium yeast tablets are rendered inactive. They are killed off by a heating process. Strains of the same yeast species are used to brew beer and bake bread.

Selenium supplementation and the risk of prostate cancer?  What do we know?  We need to be careful in interpreting the research results that we have (and we need more research), but, yes, there is evidence for an inverse association between prostate cancer risk and selenium status [Hurst 2012].

As of this writing (April 2017), the protective effect of selenium supplementation against prostate cancer seems to be found in a relatively narrow range of plasma selenium status [Hurst 2012].  Furthermore, there seems to be a U-shaped relationship between selenium status and protection against prostate cancer.

If the concentrations of selenium in the plasma are too low, there is increased risk of prostate cancer.  This is a serious concern in many regions of the world.

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Selenium and reduced risk of cancer

The results of Dr. Larry Clark’s Nutritional Prevention of Cancer trial showed the efficacy of selenium supplementation in reducing the risk of colon cancer, lung cancer, and prostate cancer. Now, a meta-analysis of 69 studies shows that higher selenium exposure is associated with reductions in the risk of breast cancer, lung cancer, and prostate cancer.

Authors of a recent meta-analysis of 69 studies of selenium exposure and cancer risk have concluded that high selenium exposure can reduce cancer risk, especially high selenium exposure that is reflected in high plasma or serum selenium status and/or in high toenail concentrations [Cai 2016].  Admittedly, higher selenium intakes (as compared to lower selenium intakes) can affect different forms of cancer differently.  We still need more research to sort out which forms and dosages of dietary and supplemental selenium are most effective at reducing cancer risk.  In this article, I want to summarize the findings of Dr. Xianlei Cai and colleagues.

What is a meta-analysis of selenium exposure and cancer risk?
A meta-analysis is a research method of combining the data from several selected research studies to reach conclusions that have greater statistical power.  In the present case, Cai et al selected 69 studies that met their inclusion criteria.  Each one of the 69 selected studies had the following characteristics:

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Daily intakes of selenium

Dietary intakes of selenium vary considerably from person to person and region to region. Selenium supplements are necessary to raise selenium status sufficiently to prevent oxidative damage to the cells, to improve immune function, and to reduce the risk of cancer and heart disease.

How much selenium from food and supplements do we need on a daily basis?  Which bio-markers of optimal selenium status seem to be most useful to answer this question?  Dr. Rachel Hurst and Dr. Susan J. Fairweather-Tait, Norwich Medical School, United Kingdom, and their colleagues set out to find answers.    The design of their study is very interesting.

They enrolled 119 healthy British men and women aged 50 – 64 years in a randomized, double-blind, placebo-controlled study that lasted 12 weeks [Hurst]. They excluded the following persons from the study:

  • smokers
  • overweight people
  • people with already high plasma selenium status
  • people with long-term illnesses
  • people on various medications
  • people unwilling to discontinue taking vitamins and herbal remedies at least one month prior to the start of the study

The 119 study participants received either placebo or one of the following treatments:

  • selenium-enriched yeast tablets containing 50, 100, or 200 micrograms of a patented organic selenium (SelenoPrecise® preparation delivered by Pharma Nord, Denmark)
  • selenium-enriched onion meals that provided the equivalent of 50 micrograms of selenium per day
  • unenriched onion meals that provided the equivalent of less than 4 micrograms of selenium per day

Measurements of selenium
Remember:
Selenium is a trace element.  We measure its intake in micrograms per day, not milligrams.  We measure selenium status in plasma and serum in terms of micrograms per liter (or equivalently, in nanograms per milliliter).  Selenium in toenails or hair, then, we measure in micrograms per gram.

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What is a high selenium yeast supplement?

Baker’s yeast and brewer’s yeast and high selenium yeast … all strains of the same species of yeast … Saccharomyces cerevisiae … High selenium yeast preparations are the most effective form of selenium supplements. The yeast in the tablets is dead and inactive. There is no risk of a yeast infection from a high selenium yeast preparation.

The trace element selenium is an essential component of the selenium-dependent enzymes called selenoproteins.  We need these selenoproteins for the optimal biological functioning of our cells.  Specifically, we need adequate daily intakes of selenium for the protection of cellular DNA, for successful reproduction, for proper thyroid gland function, for protection against infections, for anti-oxidative protection against the damage caused by free radicals, and for the prevention of cancer and heart disease.

What form of selenium is best?
Many of us cannot get enough selenium in our diets, especially if we do not regularly eat Brazil nuts (very high in selenium) or if we eat relatively little meat and fish.  However, there are various supplemental forms of selenium available to us as consumers.

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