Glycemic load, glycemic index and breast cancer risk in a prospective cohort of Swedish women.

High-glycemic load diets have been hypothesized to increase the risk of breast cancer but epidemiologic studies have yielded inconsistent findings. We examined the associations of carbohydrate intake, glycemic index and glycemic load with risk of overall and hormone receptor-defined breast cancer in the Swedish Mammography Cohort, a population-based cohort of 61,433 women who completed a food frequency questionnaire at enrollment in 1987-1990. During a mean follow-up of 17.4 years, we ascertained 2,952 incident cases of invasive breast cancer. Glycemic load but not carbohydrate intake or glycemic index was weakly positively associated with overall breast cancer risk (p for trend = 0.05). In analyses stratified by estrogen receptor (ER) and progesterone receptor (PR) status of the breast tumors, we observed statistically significant positive associations of carbohydrate intake, glycemic index and glycemic load with risk of ER+/PR- breast cancer; the multivariate relative risks comparing extreme quintiles were 1.34 [95% confidence interval (CI) = 0.93-1.94; p for trend = 0.04] for carbohydrate intake, 1.44 (95% CI = 1.06-1.97; p for trend = 0.01) for glycemic index and 1.81 (95% CI = 1.29-2.53; p for trend = 0.0008) for glycemic load. No associations were observed for ER+/PR+ or ER-/PR- breast tumors. These findings suggest that a high carbohydrate intake and diets with high glycemic index and glycemic load may increase the risk of developing ER+/PR- breast cancer.