Red meat consumption during adolescence among premenopausal women and risk of breast cancer.

BACKGROUND Adolescence may be a period of increased susceptibility to breast cancer due to regular division of undifferentiated cells that occurs between puberty and first birth. Red meat consumption during early adult life has been associated with breast cancer, but intake during adolescence has not been examined prospectively. We aimed to assess the relationship between red meat intake during adolescence and premenopausal breast cancer. METHODS We examined the incidence of invasive premenopausal breast cancer prospectively within the Nurses' Health Study II. A total of 39,268 premenopausal women who completed a validated 124-item food frequency questionnaire on their diet during high school, were followed for 7 years, from 1998 to 2005. Cox proportional hazards regression was used to estimate relative risks (RR) and 95% confidence intervals (95% CI). RESULTS 455 cases of invasive premenopausal breast cancer were diagnosed between 1998 and 2005. Compared with women in the lowest quintile of red meat intake during high school, the multivariate-adjusted RR for the highest quintile of intake was 1.34 (95% CI, 0.94-1.89; P(trend) = 0.05). A significant linear association was observed with every additional 100 g of red meat consumed per day (RR, 1.20; 95% CI, 1.00-1.43; P = 0.05). This association was more pronounced in hormone receptor-positive tumors (RR, 1.36; 95% CI, 1.08-1.70; P = 0.008) and was not significant in hormone receptor-negative tumors (RR, 0.99; 95% CI, 0.61-1.61, P = 0.97). CONCLUSION Higher red meat intake in adolescence may increase the risk of premenopausal breast cancer.