Blood sugar levels. Insulin sensitivity. Risk of diabetes. What, if anything, is the likely effect of selenium supplementation on glycemic control?
Glycemic control is the maintenance of blood sugar levels within an acceptable range to prevent the adverse effects of low blood sugar and high blood sugar.
The best measure of glycemic control is the HbA1c test. This blood test HbA1C gauges the average glucose level in the blood over a period of approximately three months. It is considered a good predictor of diabetic complications.
Type 2 Diabetes. Some news reports have suggested that high selenium intakes and status may be potential risk factors for the development of type 2 Diabetes mellitus. However, current data show that supplemental selenium does not cause diabetes [Schomburg 2020].
Two large randomized controlled trials using selenium supplements have shown no diabetes risk caused by 1) a selenomethionine product [Lippman 2009] and 2) a selenium-enriched yeast product [Thompson 2016; Jacobs 2019]. In neither study was there any significant risk of diabetes at the recommended dosage, not even among selenium-replete individuals of various ages and both genders [Schomburg 2020].
Lower selenium status during pregnancy means there is a greater risk of developing gestational diabetes [Hamdan 2022; Xu 2022]. Three different selenium biomarkers in early and late pregnancy show a quite strong association of selenium with 1) the risk of developing gestational diabetes mellitus and 2) the birth of large for gestational age offspring [Demircan 2022].
Selenium is an essential trace element, essential in the sense that our bodies cannot synthesize it, and we must get what we need of it in our diets.
Suboptimal intakes of selenium, i.e., intakes below the recommended intake levels, are associated with increased disease risks, in particular increased risk of autoimmune diseases, chronic diseases, inflammation, etc.
Unfortunately, the health risks of selenium deficiency are often neglected. Here are some facts:
Preventable endemic diseases are known in regions with selenium deficiency, e.g., in certain parts of China.
Sufficiently high selenium status is a prerequisite for adequate immune system response.
Individuals living in regions with selenium-poor soil, women who are pregnant, individuals with autoimmune thyroid disease, and individuals with a severe illness, e.g. COVID-19, are known to have sub-optimal selenium intakes and status.
Improved dietary choices and/or selenium supplementation are efficient ways to avoid severe selenium deficiency.
These are the major points in a recent journal article published by Professor Lutz Schomburg, Charité–Universitätsmedizin Berlin, Freie Universität Berlin, and Humboldt Universität zu Berlin.
Selenium and Selenoproteins
The micronutrient selenium is a component of the amino acid selenocysteine, which is itself an essential part of some 25 selenoproteins identified in human biology. Some selenoproteins are known to be essential for life; accordingly, they are preferentially synthesized and distributed. The brain, for example, has high priority for selenium in times of scarcity.read more
The long-time selenium researcher Professor Dr. Lutz Schomburg has reviewed the nutritional and preventive medicine aspects of selenium supplementation. In his mind, a selenium deficiency in and of itself constitutes a health risk that should be corrected by dietary measures or by supplemental selenium intake [Schomburg 2020].
He interprets the available evidence for positive health effects of selenium supplement as the outcome of correcting a deficiency or insufficiency of selenium.
His review of the research literature indicates that selenium supplement does not cause diabetes. Instead, the current evidence suggests that the development of type 2 diabetes with low insulin levels and high glucose levels may be causing increases in selenium levels; hence, the perceived association between the incidence of diabetes and the higher selenium status [Schomburg 2020].read more
Beneficial effect. In a 2019 study, the participants were 72 male and 22 female patients aged 48 to 64 years old with diabetes mellitus type 2. They were smokers, all of them, and they all followed a Mediterranean diet.
The findings from a 2018 meta-analysis show no consistent evidence that selenium supplementation plays a role in the development of type 2 diabetes among adults.
Researchers at the University of Arizona in Tucson, home of the Arizona Cancer Center, identified a statistically significant direct relationship between selenium and Type-2 diabetes in observational studies but no statistically significant relationship in randomized controlled trials [Kohler 2018].
Note: Randomized controlled trials are the gold standard for scientific evidence in the bio-medical field. The randomization of the study participants should produce comparable groups and should eliminate accidental bias. In observational studies, the researchers do not randomly assign the study participants to groups and do not decide which treatments each group receives or does not receive.read more
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.read more
Results from a clinical trial comparing 200 micrograms of selenium supplementation with placebo supplementation show no effect of the selenium supplementation on measures of insulin secretion and insulin action [Jacobs].
The researchers who conducted the selenium and insulin resistance study concluded that the results of the study do not show a causal role for selenium in the development of insulin resistance or in the development of type-2 diabetes [Jacobs].
Research design of the selenium and insulin resistance study
Background: In 2016, researchers at the Arizona Cancer Center in Tucson reported on the results of the Selenium Trial [Thompson].read more
Typically, the serum selenium concentration levels are significantly lower in women with gestational diabetes than in healthy pregnant women. The differences are especially remarkable in non-Caucasian pregnant women and in pregnant women in the third trimester. That is the finding of a recent meta-analysis and systematic review of the relevant literature from observational studies [Kong 2016].
Selenium and gestational diabetes
Gestational diabetes is defined as any degree of glucose intolerance that occurs with the onset of pregnancy. A physiological insulin resistance beginning in the second trimester and progressing through the third trimester is fairly typical of pregnancies. Expecting mothers generally need increased insulin secretion to maintain normal blood glucose levels. Impairment of the needed compensatory increases in insulin secretion leads to a diagnosis of gestational diabetes [Kong 2016].read more
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