No association between dietary phytoestrogens and risk of premenopausal breast cancer in a French cohort study

Abstract

Phytoestrogens, plant food components with estrogen-like biological properties, are hypothesized to contribute to the 5-fold lower breast cancer incidence in Asian compared with Western countries (1). Isoflavones comprise the phytoestrogens most abundant in soy, the traditional staple food in Asia, and a recent meta-analysis concluded that there was a slight reduction in premenopausal breast cancer risk with higher soy consumption (1). Because consumption of soy and isoflavones is typically low in Western countries, lignans and their derived metabolites, the enterolignans, might be more relevant for breast cancer prevention in these populations (2). Further large prospective studies of phytoestrogens in breast cancer are needed in Western populations to test this hypothesis. We thus examined the association between the usual dietary intake of phytoestrogens and the risk of premenopausal invasive breast cancer in a large French cohort.E3N (Etude Epidémiologique auprès de femmes de la Mutuelle Générale de l'Education Nationale) is a large ongoing prospective cohort consisting of 98,995 French women born between 1925 and 1950, subscribing to the health insurance plan for public education system employees, and who voluntarily enrolled in 1990-1991 (3). After a baseline questionnaire, follow-up questionnaires have been sent biennially to ascertain occurrence of diseases and to update menopausal status and exposure factors. Usual diet over the previous year was assessed using a…