Key Findings:
In this assessment of 11 cohort (nested case-control) and 10 case-control studies, significantly lower breast cancer risk in postmenopausal women. In limited research, a protective effect of high dietary entero lignan exposure was also shown. Inconsistent results were found for the effects of lignan on the risk of ER-positive and ER-negative breast cancer suggesting more clinical work is required. The authors also recommend the study of possible genetic modifying effects that could clarify the association between exposure to lignans and breast cancer risk.
ABSTRACT:
BACKGROUND: Epidemiologic studies that examined whether lignans, the most important class of phytoestrogens in the Western diet, protect against breast cancer have yielded inconsistent results. OBJECTIVE: In this study, we conducted meta-analyses on the association between lignans and breast cancer risk. DESIGN: We performed a systematic MEDLINE search to identify epidemiologic studies published between 1997 and August 2009. We calculated pooled risk estimates (REs) for total lignan exposure, dietary lignan intake, enterolignan exposure, and blood or urine concentrations of enterolactone and according to menopausal and estrogen receptor (ER) status of tumors. RESULTS: We included 21 studies (11 prospective cohort studies and 10 case-control studies) in the meta-analyses. Lignan exposure was not associated with an overall breast cancer risk (RE: 0.92; 95% CI: 0.81, 1.02; P for heterogeneity = 0.004). However, in postmenopausal women, high lignan intake was associated with a significant reduced risk of breast cancer (13 studies; RE: 0.86; 95% CI: 0.78, 0.94; P for heterogeneity = 0.32). Breast cancer risk was also inversely associated with enterolignan exposure (4 studies; RE: 0.84; 95% CI: 0.71, 0.97) but not with blood or urine enterolactone concentrations. The associations were not significantly different between ER-status subgroups (6 studies). CONCLUSIONS: High lignan exposure may be associated with a reduced breast cancer risk in postmenopausal women. Additional work is warranted to clarify the association between lignan exposure and breast cancer risk. (Authors Abstract)