June 12, 2000
Agricultural Research Service scientists dramatically reduced early stages of colon cancer in rats by feeding the animals broccoli grown in a high-selenium medium.
ARS nutritionists John Finley and Cindy Davis drew on reports that the form of selenium in broccoli is more potent against cancer than other food forms or selenium salts. The broccoli form is known as selenium methyl selenocysteine, or SeMSC. The body simply snips the end off this amino acid to produce the anticancer agent called methyl selenol.
The form of selenium prevalent in grains and some meats requires several chemical conversions to produce methyl selenol. Selenium salts–the forms used in some supplements–convert more readily. But it’s only one step for the form in broccoli to get there.
To test its efficacy, the researchers grew broccoli having several thousand times the selenium normally found in the vegetable. They grew the broccoli at the Grand Forks Human Nutrition Research Center in North Dakota.
Then, in a series of rat studies, they confirmed that differences in selenium metabolism translated to differences in risk of colon cancer.
First, they pitted high-selenium broccoli against the selenium salt selenate. And they made sure to control for any beneficial effects of broccoli itself, for the vegetable scores high in antioxidants and contains other substances shown to be active against cancer.
After beefing up the rats’ selenium levels for several weeks, they injected the animals with a potent carcinogen. High-selenium broccoli always resulted in fewer precancerous lesions than selenate. And the number of precancerous lesions decreased as the dose increased.
Then they confirmed the findings using a different salt–selenite–and a higher dose of selenium. They also challenged the animals with a much more potent carcinogen. Although many more precancerous lesions occurred, the rats fed high-selenium broccoli had half as many as the animals getting selenite.
More details about these studies appear in the June issue of Agricultural Research magazine online at:
ARS is USDA’s chief scientific agency.