Researchers at the University of Arizona Cancer Center in Tucson have reported interesting findings with respect to selenium supplementation [Jacobs 2019]:
- Supplementation with 200 micrograms/day of a selenized yeast preparation for 2.9 years had no effect on insulin sensitivity or beta-cell function as compared with the placebo group.
- Further stratification of the data by sex and age showed no effect modification in response to the selenium supplementation.
The Take-Home Message from this Selenium Research
- The Arizona Cancer Center research does not support the idea of a major role for selenium in insulin sensitivity or beta-cell function.
- The University of Arizona researchers write that their results provide key information for clinicians to convey to patients in the USA about the use of selenized yeast dietary supplements.
The Selenium Supplementation Research Design
The researchers analyzed the data from a subset of 400 individuals who were participating in the Selenium Trial, a randomized, double-blind, placebo-controlled trial of the effect of selenium supplementation at 200 micrograms per day on colorectal adenomatous polyps [Jacobs 2019].
The data included the fasting plasma glucose and insulin measured both before randomization and within 6 months of completing the intervention.
The researchers compared changes in the homeostasis model assessment-beta cell function (HOMA2-%beta) and insulin sensitivity (HOMA2-%S) between the active selenium treatment group and the placebo control group.
The researchers also compared the changes in the data from an oral glucose tolerance test (mOGTT) compiled for a subgroup of 175 patients (79 selenium and 96 placebo).
The Selenium Supplementation Research Results
The data showed no statistically significant differences in the changes in HOMA2-%beta or HOMA2-%S between the patients who received selenium yeast preparations compared with placebo [Jacobs 2019].
When the researchers stratified the data by the sex or age of the patients, they still did not find any statistically significant effects on insulin sensitivity by treatment group.
The Selenium Supplementation Research Conclusions
The researchers write that their findings do not support the hypothesis that there might be a significant adverse effect of supplementation with 200 micrograms/day of selenium in selenized yeast on beta-cell function or insulin sensitivity [Jacobs 2019].
Note: Insulin resistance is the bio-medical term for a failure of the body to respond well to the insulin that the pancreas makes with the consequence that glucose in the blood has a harder time entering the cells. Patients with insulin resistance may develop type 2 diabetes.
Note: Beta-cell function is the bio-medical term for the function of the pancreatic cells that synthesize and secrete insulin. Diminished beta-cell function leads to insufficient insulin secretion and to high blood sugar levels.
Modest Selenium Supplementation with no Effect on Insulin Sensitivity in Pregnant Women
Researchers in the United Kingdom measured the plasma concentration of adiponectin, which recognized as a bio-marker of insulin resistance, in the stored plasma samples taken from pregnant women in the Selenium in Pregnancy Intervention Trial (SPRINT) [Mao 2016].
In SPRINT, 230 first-time pregnant women were randomized to treatment with selenium-enriched yeast (60 micrograms/day) or placebo from 12 weeks of gestation until delivery.
- There was no significant difference in the change of adiponectin levels between the selenium and the placebo groups from week 12 to week of the pregnancy.
- There was still no significant difference in the change of adiponectin levels between the two groups when the researchers analyzed the bottom and top quartiles of baseline whole-blood selenium.
The researchers found it reassuring that a 60 mcg/day dose of selenium-enriched yeast had no adverse effect on the plasma concentrations of adiponectin in pregnant women, as adiponectin is a known bio-marker for insulin resistance [Mao 2016].
Why Researchers Choose Selenium-Enriched Yeast (High-Selenium Yeast)
Results from clinical trials have suggested that natural organic selenium-enriched yeast may be effective at reducing prostate cancer risk whereas synthetic selenomethionine seems not to be effective [Richie 2014].
In a randomized, double-blind, placebo-controlled comparison of supplementation with selenium-enriched yeast (both 200 and 285 micrograms/day) and with selenomethionine (200 micrograms/day) in 69 healthy men for 9 months, researchers demonstrated that the supplementation with selenium-enriched yeast was associated with significant reductions in bio-markers of oxidative stress whereas supplementation with selenomethionine was not [Richie 2014].
The study results suggest that selenium species other than selenomethionine may account for the reduction in oxidative stress.
The purpose of the 285-microgram dosage of the high-selenium yeast was that that dosage contained an amount of selenomethionine equivalent to the 200 micrograms of selenomethionine in the purely selenomethionine preparation. Selenium-enriched yeast preparations vary from manufacturer to manufacturer, but a good selenium-enriched preparation will contain 55-60% natural selenomethionine plus as many as 20 other selenium species in much less quantities and, at most, 1-2% inorganic selenium.
Oxidative stress is commonly defined as the excess generation of free radicals that damage cells and manipulate signal pathways. Oxidative stress has been identified as a key mechanism in insulin resistance.
Sources
Jacobs, ET, Lance, P, Mandarino LJ, … & Thompson, PA. (2019). Selenium supplementation and insulin resistance in a
randomized, clinical trial. BMJ Open Diab Res Care, 7: e000613. doi:10.1136/bmjdrc-2018-000613.
Mao, J, Bath, SC, Vanderlelie, JJ, Perkins, AV, Redman, CW, & Rayman MP. (2016). No effect of modest selenium supplementation on insulin resistance in UK pregnant women, as assessed by plasma adiponectin concentration. Br J Nutr. 2016 Jan 14;115(1):32-8. doi: 10.1017/S0007114515004067. Epub 2015 Oct 20.
Richie, JP, Das, A, Calcagnotto, AM, Sinha, R, Neidig, W, Liao, J, … & El-Bayoumy, K. (2014). 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. doi: 10.1158/1940-6207.CAPR-14-0042. Epub 2014 Jun 17.
Sies, H. (2016). The concept of oxidative stress after 30 years. In: Gelpi, R, Boveris, A, & Poderoso, J., eds. Advances in Biochemistry in Health and Disease. New York: Springer, pp. 3–11.
The information contained in this review article is not intended as medical advice and should not be used as such.
17 September 2019