Alcohol and dietary fibre intakes affect circulating sex hormones among premenopausal women

Background: The association of alcohol and fibre intake with breast cancer may be mediated by circulating sex hormone levels, which are predictors of breast cancer risk. Objective: To evaluate the relationship of alcohol and dietary fibre intake with circulating sex hormone levels among premenopausal women. Methods: A total of 205 premenopausal women completed a validated food-frequency questionnaire at baseline and after 2 years; blood samples taken at the same time were analysed for circulating sex hormone concentrations, including oestrone (E-1), oestradiol (E-2), free E-2, progesterone, androstenedione and sex hormone-binding globulin, by radioimmunoassay. We used mixed models to estimate least-square means of sex hormone concentrations for alcohol intake categories and quartiles of dietary intake. Results: After adjustment for covariates, alcohol consumption was moderately associated with higher circulating oestrogen levels; those who consumed more than one drink per day had 20% higher E-2 (P-trend = 0.07) levels than non-drinkers. In contrast, higher dietary fibre intake was associated with lower serum levels of androstenedione (28% between the lowest and highest quartiles of intake, P-trend = 0.06), but not oestrogens. Similarly, consumption of fruits (-12%, P-trend = 0.03), vegetables (29%, P-trend = 0.15) and whole grains (27%, P-trend = 0.07) showed inverse associations with androstenedione levels. Conclusions: The consistency of the observed differences in sex hormone levels associated with alcohol and fibre-rich foods indicates that these nutritional factors may affect sex hormone concentrations and play a role in breast cancer aetiology and prevention.