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Soy foods help fight breast cancer - studies

11/22/2010 12:57:00 admin

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A couple of studies have suggested that eating soy foods may not only help reduce risk of developing breast cancer in premenopausal women, but may also mitigate recurrence of the disease in prior diagnosed patients.

Here are two more studies published last year that have suggested the same thing.

One study published in the Dec 9 2009 issue of Journal of American Medical Association showed that Chinese women with breast cancer who had higher intake of soy foods like tofu were much less likely to die from the disease and had a lower risk of recurrence.

Some drugs like tamoxifen are often prescribed to breast cancer patients to minimize the effect of estrogen on the tumor growth to prevent the patients from developing contralateral breast cancer.

Soy foods contain soy isoflavones, which may compete with endogenous estrogen for receptors, leading to a decrease in the cancer-promoting effect of estrogen and there is concern that the estrogenic soy compounds may interfere with tamoxifen,according to Xiao Ou Shu, M.D., Ph.D., of Vanderbilt University Medical Center, Nashville, Tenn., author of the study.

Dr. Shu and colleagues followed 5042 female breast cancer patients aged 25 to 75 who participated in the Shanghai Breast Cancer Survival Study. Their diseases were diagnosed between March 2002 and April 2006. Patients were interviewed at 6 months, 18, 36 and 60 months after diagnosis.

During an average 3.9-year follow-up, 444 patients died and 534 recurrences of breast cancer-related deaths were identified among 5033 patients whose tumors were surgically removed.

The researchers found an inverse association between soy intake, and mortality and recurrence. Those who had the highest intake of soy protein, or soy isoflavones, were 29 percent less likely to die during the follow-up and 32 percent less likely to have breast cancer recurrence, compared to those who had the lowest intake.

After adjustment for other confounders, the 4-year mortality rates were 10.3 percent and 7.4 percent; the 4-year recurrence rates were 11.2 percent and 8.0 percent for women with the lowest and highest intakes of soy proteins, respective.

The association held true regardless of estrogen receptor status and status of tamoxifen use.

The researchers reminded readers that "The association of soy food intake with mortality and recurrence appears to follow a linear dose-response pattern until soy food intake reached 11 grams/day of soy protein; no additional benefits on mortality and recurrence were observed with higher intakes of soy food. This study suggests that moderate soy food intake is safe and potentially beneficial for women with breast cancer."

Another study published in Cancer Epidemiology, Biomarkers and Prevention found Asian-American women who had higher intake of soy during childhood were 58 percent less likely to develop breast cancer.

The possible preventative effect of soy foods, which are widely used in Asian countries, has been suspected for long as incidence of breast cancer in the U.S. has been four to seven times higher than that found in Asian countries.

"When Asian women migrate to the U.S., their breast cancer risk rises over several generations and reaches that of U.S. white women, suggesting that modifiable factors, rather than genetics, are responsible for the international differences. These lifestyle or environmental factors remain elusive; our study was designed to identify them," said Regina Ziegler, Ph.D., M.P.H., a senior investigator in the National Cancer Institute Division of Cancer Epidemiology and Genetics (DCEG).

This study involved 597 women with breast cancer and 966 healthy women of Chinese, Japanese and Filipino descent who were living in San Francisco, Oakland, Los Angeles or Hawaii.

The researchers divided soy intakes into thirds and found those whose consumption of soy foods in the highest in the adolescent and adult years were 20 to 25 percent less likely to have breast cancer, compared to those whose intake of soy foods in the lowest.

One explanation, offered by a health observer, is that when girls eat plant-protein like soy protein or tofu, they tend to eat less meat. Meat, dairy and sugar are known to promote insulin-like growth factor, which together with other hormones pushes girls to enter puberty early. Women who enter puberty early tend to have late menopause. Altogether, they have much longer exposure to high levels of cancer-promoting estrogen.

The observer also said, soy foods rich in estrogenic phytochemicals may also have a direct impact on the risk of breast cancer as well. Soy foods contain compounds that protect against angiogenesis, which would otherwise boost cancer growth.

Breast cancer is expected in one in seven women in their lifetime in the United States. The disease is diagnosed in 175,000 women and kills about 50,000 each year in the country.

Many lifestyle parameters can be modified to reduce the risk of developing breast cancer.

Jimmy Downs and editing by Rachel Stockton

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