Soy pills not helpful for breast cancer prevention, study says

Eating soy-based foods or taking soy supplements has been an intriguing strategy to reduce cancer risk. But a carefully performed new study shows soy supplements did not lower breast cancer risk and may even be harmful to some women.

Previous research has shown that people with diets high in soy have lower rates of breast cancer. Soy is also known to reduce levels of estrogen, a hormone that can contribute to breast cancer development. The new study, led by researchers at Northwestern University, was designed to look carefully at how soy consumption may change breast cells. Researchers randomly assigned 98 women at high risk for breast cancer supplements containing soy or a placebo. After six months, the women underwent a needle biopsy so that researchers could analyze levels of a protein marker of cancer cell growth, called Ki-67.

They found no significant reduction of the marker in either group. However, in premenopausal women taking the soy supplement, levels of Ki-67 rose slightly, suggesting a potential harmful effect from the supplement.

The study, published in the current issue of the journal Cancer Prevention Research, drives home a point that consistently appears in studies on nutrition and disease prevention: supplements don’t seem to have the same impact as eating whole foods that contain a blend of many nutrients.


“Although soy-based foods appear to have a protective effect, we are not seeing the same effect with supplementation using isolated components of soy, so the continued testing of soy supplements is likely not worthwhile,” the lead author of the study, Dr. Seema A. Khan, a professor of surgery, said in a news release.

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