Bioavailability of selenium from selenium‐enriched garlic

Abstract

We previously reported that garlic grown in a selenium‐fertilized medium (selenium‐enriched garlic) is superior to regular garlic in mammary cancer prevention in an animal model (Nutr Cancer 17, 279–286, 1992). The present study was designed to evaluate the nutritional bioavailability of selenium from this garlic with use of two liver selenoenzymes as biomarkers: glutathione peroxidase and type I 5'‐deiodinase. Rats were fed a selenium‐deficient diet (0.01 ppm Se) from weaning for four weeks to deplete both enzymes. They were then supplemented with nutritional levels of selenium (0.1–0.5 ppm) in the form of sodium selenite (positive control) or selenium‐enriched garlic. Our results showed that selenium‐enriched garlic was just as effective as selenite in restoring the activity of both selenoenzymes. This was demonstrated in a time course repletion experiment as well as in a dose‐response experiment. Thus the selenium in selenium‐enriched garlic has potent nutritional and anticancer efficacy. The type I 5'‐deiodinase enzyme catalyzes the conversion of thyroxine (T₄) to 3,5,3'‐triiodothyronine (T₃) and is responsible for most of the circulating T₃. Because cancer chemoprevention by selenium usually requires pharmacological levels of selenium, we also examined the possible modulation of type I 5'‐deiodinase by long‐term feeding of selenium‐enriched garlic at 3 ppm Se in the diet. The observation that a high intake of selenium‐enriched garlic did not affect 5'‐deiodinase activity suggests that its anticarcinogenic effect is unlikely to be mediated by an imbalance in the blood T₄‐to‐T₃ ratio.