Phytoestrogen Consumption and Breast Cancer Risk in a Multiethnic Population: The Bay Area Breast Cancer Study

Abstract

Research on the relation between phytoestrogens and breast cancer risk has been limited in scope. Most epidemiologic studies have involved Asian women and have examined the effects of traditional soy foods (e.g., tofu), soy protein, or urinary excretion of phytoestrogens. The present study extends this research by examining the effects of a spectrum of phytoestrogenic compounds on breast cancer risk in non-Asian US women. African-American, Latina, and White women aged 35-79 years, who were diagnosed with breast cancer between 1995 and 1998, were compared with women selected from the general population via random digit dialing. Interviews were conducted with 1,326 cases and 1,657 controls. Usual intake of specific phytoestrogenic compounds was assessed via a food frequency questionnaire and a newly developed nutrient database. Phytoestrogen intake was not associated with breast cancer risk (odds ratio = 1.0, 95% confidence interval: 0.80, 1.3 for the highest vs. lowest quartile). Results were similar for pre- and postmenopausal women, for women in each ethnic group, and for all seven phytoestrogenic compounds studied. Phytoestrogens appear to have little effect on breast cancer risk at the levels commonly consumed by non-Asian US women: an average intake equivalent to less than one serving of tofu per week.

Second primary malignancies in thyroid cancer patients

“…Other risk factors, such as diet, reproductive factors, deficiency or excess of iodine, changes in height and weight, have been involved in some studies Negri et al, 1999;Dal Maso et al, 2000;Horn-Ross et al, 2001). It is not likely that any of these factors would profoundly influence the risk related to radioiodine since we found a difference between exposed and nonexposed tumours, and, for some tumours, a dose -response relationship.…”

Epidemiology of soy exposures and breast cancer risk

“…The combined OR (summary OR ¼ 1.02, 95% CI ¼ 0.84 -1.23) from these three nested case -control studies is consistent with the finding of no association based on dietary soy isoflavones and breast cancer risk in Western populations. There were no differences in results by menopausal status (Horn-Ross et al, 2001;dos Santos Silva et al, 2004;Keinan-Boker et al, 2004;Bosetti et al, 2005;Fink et al, 2007;Verheus et al, 2007). One study examined the soy -breast cancer association by body size and reported no differences in results (Bosetti et al, 2005).…”

“…We estimated daily soy isoflavone intake in one study (Witte et al (1997) by assuming that one serving of tofu per week is 50 g and this is equivalent to 2.14 mg isoflavone per day. Francisco Bay Area, USA (Horn-Ross et al, 2001). Instead a considerable (25 -60%) proportion of soy isoflavones in these populations was from soy components added to typical Western foods including bakery and canned products.…”

“…In contrast, intake of soy isoflavones in Western populations is usually less than 1.0 mg of isoflavones per day and Asian soy foods are rarely consumed. Their sources of soy isoflavones come from some legumes, sprouts and vegetables containing small amounts of isoflavones, and from soy flour and soy protein that are commonly added as extenders and fillers in different bakery and canned goods (Horn-Ross et al, 2001). …”

“…In a few of these studies conducted in Western populations (Witte et al, 1997;Horn-Ross et al, 2001), risk patterns in relation to Asian soy foods (i.e., tofu and others) were presented. Results on these soy foods, at the relatively low levels consumed in the West, are compatible with those at corresponding consumption levels in Asian women.…”