Adolescent and Early Adulthood Dietary Carbohydrate Quantity and Quality in Relation to Breast Cancer Risk.

BACKGROUND We investigated quantity and quality of dietary carbohydrate as well as insulin load and insulin index during adolescence and also early adulthood in relation to risk of breast cancer in the Nurses' Health Study II. METHODS During 20 years of follow-up of 90,534 premenopausal women who completed a diet questionnaire in 1991, 2,833 invasive breast cancer cases were documented. In 1998, 44,263 of these women also completed a questionnaire about their diet during high school; among these women, we documented 1,118 cases of breast cancer. Multivariable-adjusted Cox proportional hazards regression was used to model relative risks (RR) and 95% confidence intervals (95% CI) for breast cancer across categories of dietary carbohydrate, glycemic index (GI), glycemic load (GL), as well as insulin load and insulin index scores. RESULTS Adolescent or early adult intakes of GI or GL were not associated with risk of breast cancer. Comparing women in the highest versus lowest quintile, the multivariable-adjusted RRs were 1.14 (0.95-1.38) for adolescent GI scores and 1.03 (0.91-1.16) for early adulthood GI scores. We also did not observe associations with insulin index and insulin load scores in adolescence or early adulthood and breast cancer risk. CONCLUSIONS We found that diets high in GI, GL, insulin index, and insulin load during adolescence or early adulthood were not associated with an increased risk of breast cancer in this cohort study. IMPACT Diets with a high glucose or insulin response in adolescence or early adulthood were not significant predictors of breast cancer incidence.