Selenium-enriched garlic is proven to be useful as a nutritional supplement in the prevention of cancer. Plants such as garlic grown in selenium-rich media contain high amounts of Se-methyl-L-selenocysteine, one of the most effective chemopreventive forms of selenium. Studies indicate that Se-methyl-L-selenocysteine is not incorporated into proteins, thereby minimizing the possibility of excessive accumulation in tissues.

The anti-carcinogenic activities of regular (grown on soil) garlic and selenium-enriched garlic (cultivated in the greenhouse) were evaluated using the 7,12-dimethylbenz[a]anthracene-(DMBA) induced mammary tumor model in rats.

The time course of mammary tumor development after DMBA administration was evaluated in rats fed with

All treatments were started 2 weeks before DMBA and continued till the end of the experiment.

Effect of Selenium species on the time course of DMBA induced mammary carcinogenesis in rats is represented in the graph below.

Animals given the Selenium-enriched garlic developed the fewest mammary tumors. However, the tissue selenium levels were found to be lower in animals fed Selenium-enriched garlic than in those fed with the same amount of selenium from Inorganic selenite.

In another experiment, laboratory rats fed with supplemental dietary Se-garlic at different levels showed consistently lower total tissue selenium accumulation than rats receiving Se-yeast. However despite this difference, Se-yeast was found to be only half as active as Se-garlic in mammary cancer prevention.

Effects of supplementation with Se-yeast and Se-garlic on mammary cancer in an animal model.

DMBA - Dimethyl –benz(a) anthracene; MNU - N-methyl-N-nitrosurea
A correlation in the difference in the biological activities of Selenium-enriched garlic and Selenium-enriched yeast and speciation differences in the chemical forms of selenium in the two natural products was evaluated.

A Selenium yeast sample that yielded 1922 micrograms/g selenium and a Selenium enriched garlic sample that yielded 296 micrograms/g were compared.

The bulk of the selenium was found to be in the form of γ-glutamyl-Se-methyl-L selenocysteine (73% of the total selenium content) in selenium garlic, and in the form of selenomethionine (85% of the total selenium content) in selenium yeast.

It was postulated that differences in the metabolism of these two compounds and their subsequent disposition in tissues might account for their differences in cancer chemopreventive activity.

A recent study hypothesizes that γ-glutamyl-Se-methyl-L-selenocysteine serves primarily as a carrier of Se-methyl-L-selenocysteine which has been demonstrated in past research to be a potent cancer chemopreventive agent in animal carcinogenesis bioassays.