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Based on the hypothesis that high-meat diets may increase breast cancer risk through hormonal pathways, the present analysis compared oestrogens in serum and urine by meat-eating status.
Intervention with repeated measures.
Two randomized soya trials (BEAN1 and BEAN2) among premenopausal healthy women.
BEAN1 participants completed seven unannounced 24 h dietary recalls and donated five blood and urine samples over 2 years. BEAN2 women provided seven recalls and three samples over 13 months. Serum samples were analysed for oestrone (E1) and oestradiol (E2) using RIA. Nine oestrogen metabolites were measured in urine by LC–MS. Semi-vegetarians included women who reported consuming <30 g of red meat, poultry and fish daily, and pescatarians those who reported consuming <20 g of meat/poultry but >10 g of fish daily. All other women were classified as non-vegetarians. We applied mixed models to compute least-square means by vegetarian status adjusted for potential confounders.
The mean age of the 272 participants was 41·9 (sd 4·5) years. Serum E1 (85 v. 100 pg/ml, P = 0·04) and E2 (140 v. 154 pg/ml, P = 0·04) levels were lower in the thirty-seven semi-vegetarians than in the 235 non-vegetarians. The sum of the nine urinary oestrogen metabolites (183 v. 200 pmol/mg creatinine, P = 0·27) and the proportions of individual oestrogens and pathways did not differ by meat-eating status. Restricting the models to the samples collected during the luteal phase strengthened the associations.
Given the limitations of the study, the lower levels of serum oestrogens in semi-vegetarians than non-vegetarians need confirmation in larger populations.
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.
To evaluate the relationship of alcohol and dietary fibre intake with circulating sex hormone levels among premenopausal women.
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 (E1), oestradiol (E2), free E2, 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.
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 E2 (Ptrend = 0.07) levels than non-drinkers. In contrast, higher dietary fibre intake was associated with lower serum levels of androstenedione (−8% between the lowest and highest quartiles of intake, Ptrend = 0.06), but not oestrogens. Similarly, consumption of fruits (−12%, Ptrend = 0.03), vegetables (−9%, Ptrend = 0.15) and whole grains (−7%, Ptrend = 0.07) showed inverse associations with androstenedione levels.
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.
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