Briefly, the data from the meta-analysis show that selenium decreases the risk of cancer at the highest daily intake levels of the included studies.
This outcome is consistent with the outcomes of a previous study showing a protective effect of selenium at high doses compared to low doses [Cai 2016]. A 2018 meta-analysis used different methods to assess selenium exposure and showed a null association between selenium at high doses compared to low doses [Vinceti 2018].
One of the big challenges in selenium research is the optimizing of the daily selenium intake to reduce the risk of prostate cancer. We need more research results to answer the following questions about the use of selenium supplements to reduce the risk of prostate cancer [Waters & Chiang 2017]:
The idea that selenium intakes and selenium status are an important determinant of prostate cancer risk began to receive considerable attention after University of Arizona Professor Larry Clark published the results of the Nutritional Prevention of Cancer Trial in JAMA in December 1996 [Clark 1996].
The Nutritional Prevention of Cancer Trial (NPCT) was a supplementation trial using 200 micrograms of a selenized yeast preparation or placebo for an average duration of 4.5 years. The study participants were 1312 men and women with an average age 63 years.
Chemotherapy and radiation continue to be the major forms of treatment for many types of cancer. The considerable toxicity of these treatments to normal cells is a problem in cancer treatment and management.
Selenium supplementation has already been associated with statistically significant reductions in the risk of various cancers and pre-cancerous conditions:
Selenium supplementation may be valuable in the treatment of cancer as well as in the prevention of cancer. Selenium has the ability to protect against the formation and progression of some cancer cells and also the ability to selectively target some existing cancer cells.
Moreover, it may be that selenium can work in synergy with conventional cancer therapies. Pre-clinical research data suggest that selenium may in some instances protect normal cells and tissues against the toxic effects of conventional cancer treatments on the cells [Evans 2017].
Higher blood selenium concentrations and higher blood selenoprotein P concentrations are significantly associated with reduced risk of high-grade prostate cancer [Outzen].
The researchers defined “advanced” prostate cancer as ≥T3 or with a Gleason-score ≥7. They defined “high-grade prostate cancer” as cancers having a Gleason score equal to or greater than 8.
Furthermore, in survival analyses, a higher pre-diagnostic level of plasma selenium is significantly associated with a lower risk of all-cause mortality in prostate cancer patients [Outzen].
These are the conclusions from an analysis of the data from the Danish “Diet, Cancer, and Health” cohort. The cohort consists of 27,179 men living in the greater metropolitan areas of Copenhagen and Aarhus who were recruited into the study. They were aged 50 – 64 years and had no previous record of cancer at the time of recruitment [Outzen].
Analysis of data from the Netherlands Cohort Study shows that higher toenail selenium concentrations are associated with a substantial reduction in the risk of advanced prostate cancer. Men in the highest quintile of toenail selenium had a statistically significant (p=0.001) 63% reduced risk of advanced (stage III-IV) prostate cancer compared to men in the lowest quintile of toenail selenium [Geybels].
Men in the highest quintile of toenail selenium concentrations had a toenail selenium level higher than 0.617 micrograms of selenium per gram of toenail. Men in the lowest quintile of toenail selenium concentrations has a toenail selenium level lower than 0.469 micrograms of selenium per gram of toenail [Geybels].
Quote: “Selenium most probably has a protective role against the development of prostate cancer and its progression to advanced stages. Therefore, selenium supplementation can be proposed for prevention of prostate cancer.”
These words are taken from the conclusion of a 2018 systematic review and meta-analysis of studies of the association between selenium and prostate cancer [Sayehmiri].
The meta-analysis is based on the data from 38 journal medical articles that included 36,419 prostate cancer cases and 105,293 healthy controls. There were 22 case-control studies, 6 cohort studies, and 10 randomized controlled trials included in the meta-analysis [Sayehmiri].
The pooled relative risk from the 38 studies of the association of selenium concentration and prostate cancer risk showed a statistically significant 14% risk reduction with higher levels of blood selenium or toe nail selenium.
Observational studies show predominantly and consistently an inverse association between selenium exposure and the risk of some cancer types [Vinceti 2018; Cai 2016]. The evidence from some 70 observational studies indicates that higher levels of exposure to selenium are associated with lower levels of cancer incidence and mortality [Vinceti 2018]. What the observational studies haven’t shown thus far is a systematic pattern suggesting specific dose-response relationships. [Vinceti 2018].
The evidence from observational studies also indicates that there may be a U-shaped form to the relationship between selenium exposure and disease risk. For example, one study suggests that the best serum selenium range for protection against prostate cancer is between 119 and 137 micrograms per liter [Chiang 2010]. A second study shows that the risk of prostate cancer decreases gradually as the selenium concentrations increase in the range from 60 micrograms of selenium per liter of plasma up to 170 micrograms per liter. Above 170 micrograms per liter, the protection ceases [Hurst 2012].
The Su.Vi.Max. study — SUpplementation en VItamines et Minéraux AntioXydants — was a big randomized, double-blind, placebo-controlled study carried out with typical French efficiency. Even though I have written the name of the study in French, there are so many English cognates that I am sure you can read the full name of the study.
The study was designed to test the health benefits of daily supplementation with a number of vitamins and minerals at nutritional dosages (roughly, one to three times the daily recommended dietary intakes) [Hercberg 1998]:
In particular, the French researchers wanted to see the effect of the daily supplementation over a long period, approximately 7.5 years, from 1994 to 2002, on the prevention of cancer and cardiovascular disease, both of which have been linked to oxidative stress and oxidative damage and might, therefore, be affected by supplementation with antioxidants.
When we test the efficacy of selenium supplementation in the prevention of cancer, we often look at the effect of the selenium supplementation on bio-markers for the development of cancer. Bio-markers are substances whose presence in blood or tissue indicates the concurrent presence of a disease or an infection.
An Indian (sub-continent) research study has shown that supplementation with selenium, zinc, riboflavin, and vitamin A significantly inhibits the development of bio-markers for oral cancers [Prasad].
Okay, because the selenium was administered as one component in a micro-nutrient cocktail, we cannot attribute the outcome solely to the selenium supplementation. But it is a good bet that the selenium – through its incorporation into antioxidant selenoproteins – was a major factor in the beneficial health effects. There is support for the idea that antioxidant supplements are effective cancer chemopreventive agents [Prasad].
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].
