gms | German Medical Science

Introduction: Several studies suggested that a high dietary intake of soy food containing isoflavones may be inversely associated with breast cancer risk. However, lignans as another class of phytoestrogens which is more common in Western diets, were rarely investigated so far. Therefore, we studied the association between exposure to lignans and breast cancer risk in a prospective cohort study.

Material and Methods: In the EPIC-Heidelberg cohort, 13,612 women (35 – 65 years) were recruited between 1994 and 1998. At baseline, habitual diet was assessed by means of a validated food frequency questionnaire. Food intake data were used to calculate the dietary intake of plant lignans (secoisolariciresinol, matairesinol) and the available amount of mammalian lignans (enterolactone, enterodiol). Until the end of 2004, 253 incident cases of invasive or in-situ breast cancer were diagnosed. We estimated odds ratios and 95 % confidence intervals by logistic regression models, adjusted for known risk factors of breast cancer as well as total energy intake. Information on menopausal status, the use of hormonal replacement therapy (HRT) at baseline, and body mass index at baseline was used for stratification.

Results: Overall, neither plant lignans nor mammalian lignans were significantly associated with breast cancer risk. After stratification for relative body weight, a high matairesinol intake was inversely associated with breast cancer risk in overweight and obese women (BMI ≥ 25 kg/m²) with an OR of 0.49 (95% CI: 0.26-0.95, p trend: 0.050). The association was not significant for secoisolariciresinol (OR=0.75; 0.43-1.29). Concerning exposure to mammalian lignans, a risk reduction with increasing amount of available enterodiol and enterolactone was found only in overweight/obese women; the association was statistically significant for enterolactone (OR=0.47, 0.25-0.89, p trend: 0.032). Among postmenopausal non-HRT users we found consistently a decreased risk of breast cancer with increasing amount of plant lignans or mammalian lignans. The association was statistically significant for the sum of mammalian lignans (OR=0.37; 0.15-0.94), comparing the extreme tertiles.

Conclusion: These results give support to the hypothesis that a high dietary intake of lignans reveal a protective effect on breast cancer risk in women. This effect seems to be restricted to women with a BMI ≥ 25 kg/m² and postmenopausal women not using HRT preparations.