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]:

If checked before a meal: From 80 to 130 mg/dL (= 4.4 to 7.2 mmol/L)
If checked two hours after a meal: Less than 180 mg/dL (< 10 mmol/L)

Meta-Analysis of Selenium Supplementation and Glycemic Control Studies

Vajdi et al investigated the effects of selenium supplementation on glycemic control parameters. Their analysis of the pooled data from 20 randomized controlled trials yielded the following results:

Selenium intake significantly reduced fasting insulin levels.
Selenium intake significantly increased quantitative insulin sensitivity check index (QUICKI) values.
Selenium supplementation did not change fasting blood sugar levels.
Selenium supplementation did not change HbA1c blood test results.
Selenium supplementation did not change HOMA-IR insulin resistance values.

Discussion: Selenium Supplementation and blood sugar Control

Selenium supplementation confers some benefits on fasting insulin and QUICKI levels compared with placebo.
Sub-group analysis revealed that selenium supplementation is associated with a significant decrease in fasting blood sugar levels among the following sub-groups:
- Participants who received 200 mcg or less of selenium supplementation
- Participants who had an intervention period of 12 weeks or less
- Participants who were under 50 years of age
- Participants who were men
- Participants who had diabetes, gestational diabetes, or prostate cancer
Administration of 200 mcg or less of selenium supplementation per day reduced fasting blood sugar more effectively than administering more than 200 mcg/day.
Sub-group analysis revealed that selenium supplementation significantly decreased HOMA-IR levels in the following circumstances:
- When the supplementation lasted at least 12 weeks
- When the participants were female
- When the participants were, under 50 years of age
- When the participants had diabetes or gestational diabetes
Sub-group analyses did not show any effect of selenium supplementation on HbA1c test results. One explanation may be that there was an insufficient number of studies conducted longer than 12 weeks.
Sub-group analysis suggested that selenium supplementation was most effective for diabetes and gestational diabetes patients. A previous study has indicated that diabetics may have a deficiency of selenium in comparison with non-diabetics. In addition, previous studies have indicated that selenium levels in the blood decrease during pregnancy.

Conclusions: Selenium Supplementation and blood sugar

The meta-analysis of the data from 20 randomized controlled trials showed that selenium supplementation is associated with a significant reduction in insulin level and a significant increase in insulin sensitivity.

In some sub-groups, selenium supplementation was also associated with an improvement in fasting blood sugar and with a reduction in insulin resistance.

Most importantly, the meta-analysis did not show any detrimental effects of selenium supplementation on biomarkers of a possible risk of developing diabetes.

Sources

CDC. Manage Blood Sugar. Centers for Disease Control and Prevention. 2022. Retrieved from https://www.cdc.gov/diabetes/managing/manage-blood-sugar.html.

Vajdi M, Hassanizadeh S, Gholami Z, Bagherniya M. Selenium supplementation effect on glycemic control: A GRADE-assessed systematic review and dose-response meta-analysis of randomized controlled trials. Pharmacol Res. 2023 Sep;195:106888.

The information presented in this review article is not intended as medical advice and should not be used as such.

15 October 2023

Milestones in early selenium research

1817 Swedish chemist Jöns Jakob Berzelius discovers selenium

1957 Biochemist Klaus Schwarz shows that selenium in microscopic amounts has a vital importance for mammalian health

1969 Professor J.T. Rotruck discovers that selenium has a biochemical role as a component of the antioxidant enzyme glutathione peroxidase

1969 Professors R.J. Shamberger and D.V. Frost report a possible protective effect of selenium against cancer in humans

1973 Professor J.T. Rotruck identifies the enzyme glutathione peroxidase as a selenium-dependent protein

1977 Professor G.N. Schrauzer publishes cancer mortality correlation studies showing an inverse correlation between dietary intakes of selenium and cancer mortality in 27 countries

1988 Professor G.Q Yang summarizes the lessons learned about the selenium-related endemic diseases Keshan disease and Kashin-Beck disease and about the importance of adequate daily selenium intakes

1989 Professor G.G. Duthie publishes evidence for a role of selenium in the prevention of cardiovascular disease

1993 Researcher W.J. Blot publishes the results of the Nutrition Intervention Trials in Linxian, China, showing that supplementation with a combination of selenium and other antioxidants reduces the risk of cancer

1994 Professor G.N. Schrauzer publishes evidence that selenium is important in the maintenance and therapy of HIV-infected patients

1996 Professor Larry Clark publishes the results of a randomized controlled trial – the Nutritional Prevention of Cancer study -- that shows selenium's cancer-protective effects on colon cancer, lung cancer, and prostate cancer

1997 Professor G.F. Combs summarizes the evidence for the protective effects of selenium against cancer

1999 Professor J.E. Oldfield publishes his Selenium World Atlas, mapping areas of selenium deficiency around the world

2000 Researcher O.A. Levander publishes evidence showing an anti-viral effect of selenium

2002 Researcher R. Gärtner shows that supplementation with selenium reduces inflammation in patients with autoimmune thyroiditis

2002 Researcher Margaret Rayman presents the arguments for increasing selenium intakes to realize selenium’s antioxidant and anti-viral and anti-inflammatory effects as well as selenium’s enhancement of immune function and reproductive success.