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].
Health Risks Associated with Selenium Deficiency
Professor Schomburg’s reading of the available literature can be summarized as follows:
- Profound selenium deficiency impairs an adequate immune response.
- Habitual low selenium intake increases thyroid disease risk, especially hypothyroidism and hyperthyroidism, and particularly in males; furthermore, certain patients with Hashimoto’s thyroiditis, Graves’ disease, or Graves’ orbitopathy respond positively to selenium supplementation.
- The lowest percentiles of selenium status are associated with an increase in cancer risks (colorectal and hepatocellular) in European subjects.
- Selenium deficiency is associated with increased risk of death in intensive care unit patients, in severe sepsis patients, and in polytrauma patients.
- Selenium deficiency is associated with increased risk of pregnancy complications.
- Selenium deficiency is associated with increased cardiovascular mortality risk, particularly in inflammatory conditions.
- Selenium deficiency is associated with a higher risk of postoperative mortality.
Selenium Status and Diabetes
Low Selenium Status and Risk of Metabolic Syndrome
Professor Schomburg’s reading of the results from the Complex Diseases in the Newfoundland Population: Environment and Genetics study in Canada (n > 3000 subjects) is that low selenium intake may be associated in a
dose-dependent manner with increased waist circumference, high BMI, and high body fat percentage, which, in turn, could mean that selenium deficiency might be a risk factor for metabolic syndrome [Schomburg 2020].
Metabolic syndrome = a combination of insulin resistance, elevated cholesterol and/or triglyceride levels, elevated fasting blood levels of glucose, and elevated blood pressure that increases the risk of cardiovascular disease
High Selenium Status and Diabetes
Professor Schomburg concludes that, collectively, the results of the Nutritional Prevention of Cancer (NPC) Trial, the Selenium and Vitamin E Cancer Prevention Trial (SELECT), and the University of Arizona Selenium Trial indicate that selenium supplementation does not exert a relevant diabetes risk, not even among well-supplied subjects, irrespective of age and gender.
Interrelationship Between Selenoprotein P and Diabetes
Professor Schomburg’s analysis of the available literature indicates that high selenium status does not increase diabetes risk but, rather, diabetes causes increasing selenoprotein P levels.
He says that the interaction between selenoprotein P and diabetes is more likely to be an induction of selenoprotein P via insulin resistance and not the other way around.
Thus, in the later stages of type 2 diabetes when insulin levels decrease due to the progressive decline in beta-cell function, the high glucose concentrations continue to promote selenoprotein P biosynthesis and secretion if not counteracted by medications such as Metformin.
Selenoprotein P = the selenoprotein containing multiple selenocysteine residues that is responsible for the transport of selenium, also to tissues such as the brain and testis.
Selenium Supplementation and Prostate Cancer
For Professor Schomburg, it is important to assess the effect of selenium supplementation in terms of the baseline selenium status of the study participants. His basic hypothesis is that the positive health effects
of selenium supplementation are restricted to patients who are poorly
supplied with selenium and who can be considered selenium-deficient and, therefore, in need of increased or supplemental selenium intake.
In looking at the outcomes of the Nutritional Prevention of Cancer (NPC) trial and the Selenium and Vitamin E Cancer Prevention Trial (SELECT), he is not surprised that significant reductions in the risk of prostate cancer were seen in the study participants whose baseline serum selenium status was below 123 micrograms per liter, i.e. below the threshold level for full expression of selenoprotein P.
Conclusion: Selenium Supplementation in regions with low dietary intakes of selenium
Professor Schomburg finds that the absence of adverse effects in selenium supplementation studies in regions with low dietary selenium intakes is compatible with the hypothesis that restoration of selenium status by supplemental selenium is safe.
He notes that supplementation studies with selenium dosages of 50–200 micrograms per day show no observation of toxicity.
Two points bear mentioning here:
- Dr. Margaret P. Rayman, Professor of Nutritional Medicine, University of Surrey, has pointed out that there seems to be a U-shaped relationship between selenium status and health. Her graph of the curve suggests that people with a selenium status below 100 mcg/L and above 170 mcg/L are more likely to suffer health problems.
- Dr. John P. Richie Jr and colleagues at Pennsylvania State University in Hershey have shown that a high-selenium yeast supplement protects against oxidative stress better than a pure selenomethionine supplement does.
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Richie JP Jr, Das A, Calcagnotto AM, Sinha R, Neidig W, Liao J, Lengerich EJ, Berg A, Hartman TJ, Ciccarella A, Baker A, Kaag MG, Goodin S, DiPaola RS, El-Bayoumy K. 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.
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The information presented in this review article is not intended as medical advice and should not be construed as such.
15 February 2021