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Soy Appears Safe for Breast Cancer Survivors

Moderate Intake of Soy Reduced Breast Cancer Death Risk, Recurrence in Study
By
WebMD Health News
Reviewed by Louise Chang, MD

soy_cuts_breast_ca_risk_1.jpg

Dec. 8, 2009 -- Moderate intake of soy foods by breast cancer survivors appears to be not only safe but beneficial, according to a new study.

''Women who had a higher soy intake had a lower mortality and lower risk of relapse [than women with a low intake]," says researcher Xiao Ou Shu, MD, PhD, professor of medicine at Vanderbilt University Medical Center in Nashville, Tenn.

Previous research has yielded conflicting findings, with some studies finding that soy foods reduce breast cancer risk but others finding that genistein, an estrogen-like compound known as an isoflavone in soy, helps breast cancer cells grow in the lab and promotes tumor growth in animals.

"Some papers say it's safe for women [with breast cancer] to eat some form of soy, others say [these] women should be cautious," Shu tells WebMD. Her findings, she says, should be reassuring to breast cancer survivors.

But the new study isn't the final word, says an expert who co-authored an editorial accompanying the study, both published in the Journal of the American Medical Association. She cites a relatively short follow-up of four years, along with differences in soy consumption habits of women in the U.S. and women in the study, who were from China.

Soy and Breast Cancer: Study Details

Shu and her colleagues analyzed data from the Shanghai Breast Cancer Survival Study, following 5,042 women who were ages 20 to 75 when diagnosed with breast cancer between March 2002 and April 2006.

Follow-up continued through June 2009, with the researchers analyzing information on the diagnosis, cancer stage, treatment, disease progression, and intake of soy foods. The researchers estimated the nutrients consumed -- including both soy protein and isoflavone intake.

After a median follow-up of nearly four years, 444 women had died (from any cause) and 534 had recurrences or breast cancer-related deaths. The researchers looked at the connections between soy intakes and outcomes.

Soy foods are rich in the phytoestrogens known as isoflavones. Because they are estrogen-like, some experts think they compete with the body's estrogen, thus keeping the overall estrogen in the body low. But others worry these isoflavones may exert an estrogen-like effect, perhaps boosting the risk of cancer recurrence.

Soy and Breast Cancer: Study Results

Women in the group with the highest intake of soy had a 29% lower risk of death during the study and a 32% lower risk of breast cancer recurrence, compared to women in the group with the lowest intake.

At the four-year follow-up,10.3% of the women in the lowest intake group had died, but 7.4% of those in the highest intake group. Although 11.2% of those in the lowest intake groups had recurrences, 8% of those in the highest group did.

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