Increased risk of breast cancer with high levels of soy consumption

This study was published in Cancer Epidemiology, Biomarkers and Prevention 2004 May;13(5):698-708

Study title and authors:
Phytoestrogen concentrations in serum and spot urine as biomarkers for dietary phytoestrogen intake and their relation to breast cancer risk in European prospective investigation of cancer and nutrition-norfolk.

Grace PB, Taylor JI, Low YL, Luben RN, Mulligan AA, Botting NP, Dowsett M, Welch AA, Khaw KT, Wareham NJ, Day NE, Bingham SA.
MRC Dunn Human Nutrition Unit, Wellcome Trust/MRC Building, Hills Road, Cambridge CB2 2XY, United Kingdom.

This study can be accessed at: http://www.ncbi.nlm.nih.gov/pubmed/15159299

The study investigated the association between soy phytoestrogens (such as daidzein and genistein) and breast cancer. The study included 333 women (aged 45-75 years) who were followed for up to eight years.

The study found:
(a) Women who consumed the highest levels of daidzein had a 17.6% increased risk of breast cancer compared to women who consumed the lowest levels of daidzein.
(b) Women who consumed the highest levels of genistein had a 16.5% increased risk of breast cancer compared to women who consumed the lowest levels of genistein.

The results from the study show that high dietary intake of soy (daidzein and genistein) are associated with an increased risk of breast cancer.