Key Findings
In this study, data from a large cohort of French women was used to prospectively investigate the association between dietary lignans at intake levels typically found in Western diets and the risk of breast cancer. Associations were assessed between the risk of postmenopausal invasive breast cancer and the usual dietary intakes of four plant lignans (i.e., pinoresinol, lariciresinol, secoisolariciresinol, and matairesinol). Associations were examined between postmenopausal invasive breast cancer risk and estimated exposures to two enterolignans (i.e., enterodiol and enterolactone), as assessed through a validated dietary questionnaire. The results of this large prospective study of French women showed that higher dietary intakes of lignans were associated with a reduction in the risk of postmenopausal breast cancers, particularly those positive for both ER and PR. Increasing dietary lignan intake may be a potential preventive approach. In particular, individual differences in the metabolism of plant lignans into enterolignans and the mechanisms behind the potential biologic actions of enterolignans in breast carcinogenesis need to be better understood.
ABSTRACT
Background Studies conducted in Asian populations have suggested that high consumption of soy-based foods that are rich in isoflavone phytoestrogens is associated with a reduced risk of breast cancer. However, the potential associations of other dietary phytoestrogens — i.e., the lignans or their bioactive metabolites, the enterolignans — with the risk of breast cancer are unclear. Methods We prospectively examined associations between the risk of postmenopausal invasive breast cancer and dietary intakes of four plant lignans (pinoresinol, lariciresinol, secoisolariciresinol, and matairesinol) and estimated exposure to two enterolignans (enterodiol and enterolactone), as measured with a self administered diet history questionnaire, among 58 049 postmenopausal French women who were not taking soy isoflavone supplements. Relative risks (RRs) and 95% confidence intervals (CIs) were estimated using multivariable Cox proportional hazards regression models. Analyses were further stratified by the combined estrogen and progesterone receptor (ER/PR) status of the tumors. Statistical tests were two-sided. Results During 383 425 person-years of follow-up (median follow-up, 7.7 years), 1469 cases of breast cancer were diagnosed. Compared with women in the lowest intake quartiles, those in the highest quartile of total lignan intake (>1395 μ g/day) had a reduced risk of breast cancer (RR = 0.83, 95% CI = 0.71 to 0.95, P trend = .02, 376 versus 411 cases per 100 000 person-years), as did those in the highest quartile of lariciresinol intake (RR = 0.82, 95% CI = 0.71 to 0.95, P trend = .01). The inverse associations between phytoestrogen intakes and postmenopausal breast cancer risk were limited to ER- and PR-positive disease (e.g., RR for highest versus lowest quartiles of total plant lignan intake = 0.72, 95% CI = 0.58 to 0.88, P trend = .01, 174 versus 214 cases per 100 000 person-years, and RR for highest versus lowest quartiles of total enterolignan level = 0.77, 95% CI = 0.62 to 0.95, P trend = .01, 164 versus 204 cases per 100 000 person-years). Conclusions High dietary intakes of plant lignans and high exposure to enterolignans were associated with reduced risks of ER- and PR-positive postmenopausal breast cancer in a Western population that does not consume a diet rich in soy.
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