Circulating enterolactone and risk of breast cancer: a prospective study in New York

It has been proposed that phyto-oestrogens protect against breast cancer. Lignans are the main class of phyto-oestrogens in Western diets. We conducted a case–control study of breast cancer

and serum levels of the main human lignan, enterolactone, nested within a prospective cohort study, the New York University Women's Health Study. Serum samples collected at enrollment and

stored at −80°C were used. Among 14 275 participants, 417 incident breast cancer cases were diagnosed a median of 5.1 years after enrollment. Cohort members individually matched to the cases

on age, menopausal status at enrollment, serum storage duration and, if premenopausal, day of menstrual cycle were selected as controls. No difference in serum enterolactone was observed

between postmenopausal cases (median, 14.3 nmol l−1) and controls (14.5 nmol l−1), whereas premenopausal cases had higher levels (13.9 nmol l−1) than their matched controls (10.9 nmol l−1,

P-value=0.01). In the latter group, the odds ratio for the highest vs the lowest quintile of enterolactone was 1.7 (95% confidence interval (CI), 0.8–3.4; P-value for trend=0.05) and after

adjustment for known risk factors for breast cancer was 1.6 (95% CI, 0.7–3.4; P-value for trend=0.13). We observed a moderate positive correlation between serum enterolactone and serum sex

hormone-binding globulin in postmenopausal women (r=0.29 in controls (P