Soy Might Lower Postmenopausal Breast Cancer Recurrence
Posted Oct 20 2010 5:45am
Soy is one of the most researched foods in regards to potential health benefits. Lower incidences of diseases like cardiovascular disease, prostate cancer, and breast cancer in countries were soy is typically eaten in much higher amounts than here in the U.S. caused scientists to explore soy's possible role in human health. While many of these research studies have suggested that soy consumption might support normal heart health and help relieve menopausal discomforts, the possible benefits of soy consumption for breast cancer risk has remained controversial. This controversy centers on the fact that the soy isoflavones (genistein, daidzein, and glycitein) found naturally in soybeans have a chemical structure similar to estrogen and can act in some cases like a weak estrogen. This has caused many people to become concerned about the effect soy and soy isoflavones might have on estrogen-dependent diseases like estrogen-receptor positive breast cancer. However, research over the last two years suggests that dietary soy consumption might be beneficial for breast cancer patients.
The latest breast cancer research study (free to download), published online ahead of print in the Canadian Medical Association Journal, explored the impact of dietary soy isoflavone consumption on breast cancer recurrence in Chinese women. From mid-2002 to mid-2003 breast cancer researchers recruited women diagnosed with early or local advanced breast cancer and being treated with endocrine therapy after surgery. The 524 breast cancer patients who volunteered completed a questionnaire designed to determine their usual diet and exercise habits, including their consumption of soy foods. Based on their soy consumption, the breast cancer patients were categorized into four groups ranging from low soy consumption to high soy consumption. These breast cancer patients were followed for 5 years and incidence of breast cancer recurrence and death recorded. The relationships between soy isoflavone consumption and breast cancer recurrence were analyzed. The results of this analysis showed
62% of soy isoflavone intake was in the form of soymilk (26%), tofu (21%), and soy flour (15%) for an average daily intake of about 26 mg soy isoflavones per day overall.
When categorized into groups based on their levels of consumption, the group with the lowest soy isoflavone intake consumed only about 6.5 mg/day on average. The group with the highest soy isoflavone intake consumed about 50 mg/day on average.
There was no apparent link between soy isoflavone consumption and breast cancer recurrence or death in premenopausal Chinese women.
Postmenopausal women with the highest quarter of soy isoflavone consumption had a 33% reduction in breast cancer recurrence overall compared to postmenopausal women with low dietary isoflavone intake.
ER+/PR+ breast cancer recurrence was 13% lower in postmenopausal women with higher levels of soy isoflavone intake (more than 42 mg/day) compared to postmenopausal women in the lowest quarter of soy isoflavone consumption.
Among postmenopausal women treated with anastrozole, an aromatase inhibitor, the women in the high soy isoflavone intake group had a 35% lower risk of breast cancer recurrence compared to the women in the soy intake group.
There was no relationship between soy isoflavone consumption and death in the postmenopausal women.
These are very interesting results that confirm two other studies published in the last year. This new breast cancer research study suggests that not only is soy consumption potentially safe for breast cancer patients, but it might reduce the risk of breast cancer recurrence when consumed at levels greater than 42 mg soy isoflavones/day. Similarly, the Shanghai Breast Cancer Survival Study (free to download) reported that the highest quartile of soy protein intake (more than 15 grams per day) was linked to about a 29% reduction in the risk of death and a 32% reduction in the risk of breast cancer recurrence in breast cancer survivors. A third breast cancer research study in mostly Caucasian breast cancer survivors, the Life After Cancer Epidemiology study, reported that increasing levels of daidzein and glycitein consumption tended to be linked to a reduced risk of breast cancer recurrence in postmenopausal women with the greatest risk reduction observed in tamoxifen users.
Overall, these new studies suggest that soy consumption might be beneficial for some breast cancer survivors. This appears to depend on menopausal status and/or hormonal environment. Additional research will be needed to determine what populations of people can benefit the most from adding soy to their diet and if there is an optimum time to start considering soy as part of one's regular diet. In this latter regard, some studies suggest that adding soy to one's diet as a teen might have the most cancer fighting benefits.