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.
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
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