Adolescent diet and risk of breast cancer

Objectives: To investigate the components of adolescent diet that may influence risk of breast cancer as an adult. Methods: Retrospective cohort study among 47,355 participants in the Nurses Health Study II who answered a 131-item food frequency questionnaire about diet during high school. Cox proportional hazards regression was used to estimate relative risks and 95% confidence intervals among incident cases of breast cancer between 1989 (inception of the study) and 1998 (when high school diet was assessed). Results: Intakes of fat and fiber were not significantly related to risk of breast cancer in multivariate analysis, but increased intake of vegetable fat (Q(5) versus Q(1) multivariate RR = 0.58, 95% CI (0.38-0.86); test for trend p = 0.005) and vitamin E (Q(5) versus Q(1) multivariate RR = 0.61, 95% CI (0.42-0.89); test for trend p = 0.003) were associated with a lower risk. A higher dietary glycemic index (Q(5) versus Q(1) multivariate RR = 1.47, 95% CI (1.04-2.08); test for trend p = 0.01) was associated with increased risk of breast cancer. Conclusions: The apparent protective effects of vegetable fat and vitamin E and adverse effect of high glycemic foods on risk of breast cancer need confirmation in prospective analyses.