Selenium is found in soil, and human consumption comes by eating plants that have absorbed the nutrient or fish or animals that have eaten plants as part of their diet. "The content of selenium in the food depends on the soil content of this trace element, and in the same country there are areas at high, adequate or low content of selenium in the soil," said the study's lead author, Dr. Luigina Bonelli, head of the unit of secondary prevention and screening at the National Institute for Cancer Research in Genoa, Italy.
Earlier research had suggested that selenium can inhibit cell proliferation in the colon and rectum, Bonelli said.
Michele Forman, a professor of epidemiology at the M.D. Anderson Cancer Center in Houston, said that, though the findings are interesting, it's impossible to tell if the benefit was attributable to the selenium or to the other vitamins and minerals included in the supplement.
"You really don't know if it's the selenium or some combination that reduces risk of recurrence," Forman said.
In addition, the daily dosages of vitamins A and E taken by the participants were higher than the recommended daily allowances, Forman added. High levels of such vitamins can be detrimental, she said.
In the omega-3 study, U.S. researchers surveyed 1,509 whites and 369 blacks about their dietary habits in the past year. About half of the participants had colorectal cancer.
Among the white participants, those whose diets were in the highest fourth of omega-3 fatty acid consumption were 39 percent less likely to have colorectal cancer than those in the lowest fourth. However, for reasons the authors said they did not know, no association was noted between omega-3s and a reduction of colorectal cancer risk among black participants. The disease occurs at a higher rate among b
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