Dietary glycemic load (GL), glycemic index (GI), and
carbohydrate could be associated with
breast cancer risk by influencing long-term
blood glucose and
insulin concentrations. We examined associations between GL, GI, and
carbohydrate and incident
breast cancer in 148,767 Women's Heath Initiative (WHI) participants. Dietary variables were estimated from food frequency questionnaires administered at baseline. Self-reported breast
cancers during follow-up were confirmed by medical records review. Cox proportional hazards regression modeled time to
breast cancer within quintiles of GL, GI, and
carbohydrate. There were 6,115 total breast
cancers after a median follow-up of 8.0 yr. We observed no associations between GL, GI, or
carbohydrate and total incident
breast cancer, with hazard ratios and 95% confidence intervals for the highest vs. lowest quintiles of 1.08, 0.92-1.29 (P for trend = 0.27); 1.01, 0.91-1.12 (P = 0.74); and 0.95, 0.80-1.14 (P = 0.98), respectively. There was a trend toward significance for the positive association between GL and in situ
cancers (1.40, 0.94-2.13; P = 0.07). Although there was no evidence of associations between GL, GI, or
carbohydrate and total
breast cancer risk in WHI participants, the suggestion of an association between GL and risk of in situ
cancers requires further investigation.