Although the study did not address the link between soy use and breast cancer recurrence, Clarke and Hilakivi-Clarke again cautioned against overuse of soy supplements, particularly by women at high risk for breast cancer or breast cancer survivors.
In the same way that estrogen-based hormone replacement therapy may be contraindicated for some women at high risk to develop breast cancer, soy isoflavone supplementation may not be a good idea for these women either, the researchers said. Co-author Bruce Trock, PhD, of the Johns Hopkins School of Medicine added, "High-dose soy or isoflavone supplements have biological effects that are different from normal soy foods, and no one has studied the effect of long-term consumption of such supplements."
"Soy foods like tofu and soy milk are readily available now if women want to add them to their diet," Trock said.
Because soy has recently become a widely used food additive in the United States, many Americans get some soy that they are not aware of, said Hilakivi-Clarke. "Our data suggests that women do not need to consume very much soy to possibly benefit from it. Higher soy intake does not provide additional risk reduction," she said.
To conduct the meta-analysis, Clarke, Hilakivi-Clarke, and Trock looked at 18 epidemiologic studies published between 1978 and 2004 that examined the association between soy intake and breast cancer risk. Some of these studies were based on the hypothesis that Asian women have reduced incidence of breast cancer, compared to American women, because they have traditionally eaten a diet rich in soy foods, such as tofu. In some studies, soy foods were just one of the food items studied in connection to
Contact: Liz McDonald
Georgetown University Medical Center