Soy food consumption reduces the risk of death in breast cancer survivors. - GreenMedInfo Summary
Soy food consumption and breast cancer prognosis.
Cancer Epidemiol Biomarkers Prev. 2011 Feb 25. Epub 2011 Feb 25. PMID: 21357380
1Division of Research, Kaiser Permanente.
BACKGROUND: Contrary to earlier clinical studies suggesting soy may promote breast tumor growth, two recent studies demonstrate that soy-containing foods are not adversely related to breast cancer prognosis. Using data from the Women's Healthy Eating and Living (WHEL) study, we examined the effect of soy intake on breast cancer prognosis. METHODS: 3088 breast cancer survivors, diagnosed between 1991 and 2000 with early stage breast cancer and participating in WHEL were followed for a median of 7.3 years. Isoflavone intakes were measured post-diagnosis using a food frequency questionnaire (FFQ). Women self-reported new outcome events semi-annually which were then verified by medical records and/or death certificates. Hazard ratios (HR) and 95% confidence intervals (CI) representing the association between either a second breast cancer event or death and soy intake were computed, adjusting for study group and other covariates using the delayed entry Cox proportional hazards model. RESULTS: As isoflavone intake increased, risk of death decreased (p for trend=0.02). Women at the highest levels of isoflavone intake (>16.3 mg isoflavones) - had a non-significant 54% reduction in risk of death.CONCLUSIONS: Our study is the third epidemiological study to report no adverse effects of soy foods on breast cancer prognosis. Impact: These studies, taken together, which vary in ethnic composition (two from the US and one from China) and by level and type of soy consumption, provide the necessary epidemiological evidence that clinicians no longer need to advise against soy consumption for women diagnosed with breast cancer.