Goodman MT, Shvestsov YB, Wilkens LR et al.
University of Hawaii, Honolulu, HI, USA.
Cancer Prev Res 2009;2:887–94.
Editor’s note: Phytoestrogens are naturally occurring, non-steroidal plant compounds with a variety of biological activities that may influence the risk of breast cancer. Phytoestrogens are hypothesized to reduce the levels of biologically available estrogen through the stimulation of sex hormone-binding globulin production or competitive binding of the estrogen receptor. Epidemiological studies of the association between dietary isoflavone and lignan consumption and the risk of breast cancer have been combined recently in two meta-analyses. In the first of these, Trock et al. reported a modest but statistically significant 14% reduction in breast cancer risk among women with a high soy intake compared with women with a low intake (
J Natl Cancer Inst 2006;98:459–71). In the second, Wu et al. found a significant reduction in the risk of breast cancer among Asian women reporting a high soy intake compared with women reporting a low intake, but this was not found among non-Asian women (
Br J Cancer 2008;98:9–14). These meta-analyses suggest that the beneficial effects of soy against breast cancer may only occur at relatively high levels of consumption. The results of prospective investigations of the association between blood or urine levels of phytoestrogens and breast cancer risk conducted to date have been inconclusive. The objective of the present study was to examine the association between the major urinary phytoestrogens daidzein, genistein, equol, and enterolactone and the risk of postmenopausal breast cancer in a multiethnic population with a wide range of dietary intakes, including Japanese Americans with a relatively high intake of soy products.