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Selenium and diabetes.

Sixty patients (mean age, 55 years) with type 2 diabetes who were being treated with oral hypoglycemic agents were randomly assigned to receive, in double-blind fashion, 200 [micro]g per day of selenium (as sodium selenite) or placebo for 3 months. At baseline, the mean serum selenium concentration in the selenium group was 42.7 [micro]g/L, as compared with a mean of 101 [micro]g/L in healthy individuals living in the same region. The mean fasting plasma glucose concentration increased in the selenium group from 132 mg/dl at baseline to 148 mg/dl, whereas it decreased in the placebo group from 150 mg/dl to 130 mg/dl (p < 0.01 for the difference in the change between groups). The mean HbA1c level decreased in the selenium group from 7.21 % at baseline to 6.83%, and in the placebo group it decreased from 7.80% to 6.54% (p < 0.01 for the difference in the change between groups). The mean HDL cholesterol level increased in the selenium group from 42.5 mg/dl at baseline to 46.2 mg/dl, and in the placebo group it decreased slightly (p = 0.04 for the difference in the change between groups).

Comment: While the increase in HDL-cholesterol levels in the selenium group might predict lower cardiovascular disease risk, the adverse changes in glycemic control compared with placebo is cause for concern. However, it would be premature to recommend that patients with diabetes avoid selenium supplements. Selenium levels tend to be low in people with type 2 diabetes, and selenium deficiency is a known cause of cardiomyopathy. It is therefore possible that selenium could help prevent the cardiomyopathy that is associated with diabetes.

It is difficult to understand how the selenium group could have shown both an increase in fasting plasma glucose levels (suggesting worse diabetic control) and a decrease in HbA1c levels (suggesting better diabetic control). One possible explanation is that selenium supplementation actually exerted an antidiabetic (glucose-lowering) effect or enhanced the effect of the oral hypoglycemic drugs, which led to nocturnal hypoglycemia followed by rebound hyperglycemia in the morning. This phenomenon has been described previously, and is known as the Somogyi effect. When worsening morning hyperglycemia is caused by nocturnal hypoglycemia, it can be improved by lowering, not increasing, the dosage of antidiabetes medication. This explanation for the worsening morning glucose levels in the selenium group is supported by the results of animal studies, in which selenium supplementation improved glucose metabolism. Longer-term studies are needed to determine what effect selenium supplementation has on outcomes such as cardiovascular disease and mortality in people with diabetes.

Faghihi T et al. A randomized, placebo-controlled trial of selenium supplementation in patients with type 2 diabetes: effects on glucose homeostasis, oxidative stress, and lipid profile. Am J Ther. Epub 2013 Apr 9.

by Alan R. Gaby, MD

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Title Annotation:Literature Review & Commentary
Author:Gaby, Alan R.
Publication:Townsend Letter
Article Type:Abstract
Date:Jan 1, 2014
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