Blood Sugar Control and Selenium Supplementation

Blood sugar levels. Insulin sensitivity. Risk of diabetes. What, if anything, is the likely effect of selenium supplementation on glycemic control?

Blood sugar monitor
To maintain blood sugar levels within the normal range, the CDC recommends eating at regular times, not skipping meals, eating foods lower in calories, saturated fat, trans fat, sugar, and salt, drinking water instead of juice or soda, limiting alcohol intake, and exercising. Adequate intakes of selenium are also important.

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.

Checking Blood Sugar

The US Center for Disease Control and Prevention suggests that logical times for testing blood sugar levels are as follows [CDC 2022]:

  • When first awake and before eating or drinking anything
  • Before a meal
  • Two hours after a meal
  • At bedtime
Target Blood Sugar Levels

The CDC suggests the following desirable blood sugar levels [CDC 2022]: read more

Selenium and Type 2 Diabetes

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].

Diabetes symptoms
It seems likely that diabetes causes elevated blood selenium levels rather than the other way around [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].

Moreover, in the Selenium Trial, the researchers saw no causal role for selenium in the development of insulin resistance or diabetes. Instead, they observed decreased fasting blood glucose levels in the selenium supplemented group compared to the control group [Jacobs 2019]. read more

Selenium Status and the Risk of Gestational Diabetes

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].

Storks on a nest
Low maternal selenium status is strongly associated with an increased risk of gestational diabetes and with an increased risk of large for gestational age offspring.

The Mayo Clinic defines gestational diabetes as being diagnosed with diabetes for the first time during pregnancy. Gestational diabetes is like other forms of diabetes in that it affects how well the cells use glucose. It causes high blood sugar levels that can affect the mother’s health and the baby’s health [Mayo Clinic 2023]. read more

Low Selenium Status and Autoimmune Diseases

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.

Elderly people
Professor Schomburg distinguishes between selenium substitution – supplying selenium to correct a nutritional deficit – and selenium supplementation – supplying selenium on top of a sufficient baseline status for therapeutical purposes. Here, elderly people with joint pain.

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

Selenium as a Nutritional and Preventive Medicine Substance

Berlin Brandenburger Tor
Professor Dr. Lutz Schomburg, affiliated with the Charité Institute of Experimental Endocrinology and with both the Humboldt University and the Free University in Berlin, has analyzed the research literature on selenium supplementation. He concludes that current data show that selenium supplementation does not cause diabetes.

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

Selenium Supplementation and Blood Sugar Levels

Testing blood sugar
The results of randomized controlled trials of selenium supplementation show beneficial effects or no effect on blood sugar levels and insulin sensitivity values. In this review, we summarize the study results.

The effect of selenium supplementation on blood sugar levels and on the risk of diabetes is still an open question. However, the data from randomized controlled studies show that selenium supplementation is associated with either a beneficial effect or no effect at all on blood sugar levels, insulin sensitivity, and glucose tolerance [Jablonska 2016].

Study Participants with Type-2 Diabetes

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 researchers administered selenium 200 microg/day once daily on an empty stomach. The study data showed a statistically significant reduction in the blood levels of glucose and in HbA1c values at both three months and six months after the beginning of the treatment. The administration of selenium to type-2 diabetic patients seemed to improve the patients’ glycemic profile [Karalis 2019]. read more

Selenium Supplementation and Glucose Metabolism

The evidence from a randomized controlled trial shows that 2.9 years of supplementation with 200 micrograms per day had no effect on insulin sensitivity and no effect on pancreatic beta-cell function compared with placebo [Jacobs 2019]. The evidence from randomized controlled trials does not support a role for selenium in the risk of developing type-2 diabetes [Kohler 2018].
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

Selenium Supplementation: No Adverse Effect on Insulin Resistance

Researchers at the Arizona Cancer Center report study results that do not support any significant adverse effect of daily supplementation with 200 micrograms/day of selenized yeast on beta-cell function or insulin sensitivity. High-selenium yeast preparations contain more selenium species with more biological functions than the 100% selenomethionine preparations do.

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. read more

Selenium supplementation and insulin resistance: a clinical study

The latest clinical evidence shows that selenium supplementation of older adults with 200 micrograms of a high-selenium yeast preparation for up to three years does not adversely affect pancreatic beta-cell function or insulin sensitivity.

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]. 

These results can be regarded as important evidence that selenium supplementation for up to three years in older individuals has no diabetes causing effects in humans [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

Serum selenium status and gestational diabetes

The prevalence of gestational diabetes varies from region to region of the world from below 5% of pregnancies to below 10% to as high as 20%. Gestational diabetes increases the risk of type 2 diabetes and metabolic syndrome for the mother and increases the risk of acute and long-term adverse metabolic disorders in the offspring. A recent meta-analysis reveals that women with gestational diabetes typically have significantly lower serum selenium concentrations.

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