The association between phytoestrogen intake and breast cancer in postmenopausal women

Breast cancer is the second leading cause of death in women in the U.S. The CDC estimates that between 2010 and 2020, there will be an increase in breast cancer in women in the United States by 21%, or greater 900,000 new cases per year. (CDC) Women are at increased risk for breast cancer due to the fact that some breast cancers have cells which are responsive to the hormone estrogen. Further, the risk of developing cancer increases as women age. Women who experience menopause after age 55 have an increased risk of developing breast cancer. (Surakasula et al., 2014) Phytoestrogens, which include isoflavones, are compounds found in plants and processed foods, which structurally and functionally mimic the hormone estrogen. Soy is frequently found in processed foods regularly consumed in the average American diet and is a source of isoflavones, including genistein, daidzein, and daidzein’s metabolite, equol. Phytoestrogens can bind to the estrogen receptor and change the expression of genes that respond to estrogen, such as the oncogene c-Fos, a protein in breast cancer cells which can suppress breast cancer cell growth when it is mutated (Lu et al., 2005). Phytoestrogens have been shown to reduce the severity and frequency of some of the symptoms of menopause, including a reduction in hot flashes and other estrogen deficiency-related symptoms of menopause. (Chen et al., 2015). Phytoestrogens have been used therapeutically in menopausal women, as they can compensate for lower levels of estrogen in the body. There is, however, limited research regarding the consumption of soy and increased risk for cancer in postmenopausal women. The objective of this study was to determine whether increasing levels of urinary phytoestrogen are correlated with a decreased risk of postmenopausal breast cancer. The analysis observes 2,439 postmenopausal female subjects equal to or greater than 45 years of age who had urinary phytoestrogen and reproductive health data in the 1999-2010 National Health and Nutrition Examination Survey database. The dietary data was obtained from the U.S. Department of Agriculture’s Agricultural Research Service database. Logistic regression models constructed using SAS were used to assess the change in the relative risk for cancer across low, medium, and high levels of urinary daidzein, genistein, and equol. Variables of interest, including demographic, body measures, dietary patterns, and lab measures, were compared to a base model, which adjusts for age only. It was found that the relative risk for postmenopausal breast cancer was not significantly different in the tertiles and quintiles of urinary phytoestrogens. The greatest increase in the likelihood of postmenopausal breast cancer was found to be 1.53 times in the second tertile of daidzein, increasing the risk by 53%. There was no significant protective effect of increasing levels of urinary phytoestrogens against postmenopausal breast cancer