Correspondence re: C. R. Jonas et al., Dietary glycemic index, glycemic load, and risk of incident breast cancer in postmenopausal women. Cancer Epidemiol. Biomark. Prev., 12: 573-577, 2003.

We read with interest the article by C. R. Jonas et al. showing no association between dietary glycemic index or glycemic load and breast cancer in the Cancer Prevention Study II Nutrition Cohort. We similarly examined the relation between usual glycemic index and load derived from a food frequency questionnaire (1) over 15 years of follow-up (1986–2000) in 34,703 postmenopausal women initially free of cancer in the Iowa Women’s Health Study. After adjustment for baseline age, energy intake, body mass index, alcohol intake, parity, age at first live birth, age at menopause, family history of breast cancer, hormone replacement therapy, and physical activity, the relative risks of incident breast cancer (n 2031 events) across quartiles were 1.0, 1.06, 1.13, and 0.95 (P for trend 0.67) for baseline glycemic index and 1.0, 0.98, 0.99, and 1.01 (P for trend 0.89) for baseline glycemic load. There also was no association (P for trend 0.40) in models adjusting only for age and energy intake. Our results in postmenopausal women corroborate those of Jonas et al., suggesting the glycemic index or load of the usual diet is not a risk factor for breast cancer.