Glycemic load, glycemic index linked to breast cancer risk

NEW YORK (Reuters Health) - Carbohydrate intake, glycemic load, and glycemic index are associated with the risk of estrogen receptor (ER)+/progesterone receptor (PR)- breast cancer, Swedish researchers say.

Dr. Susanna C. Larsson of Karolinska Institute in Stockholm and colleagues analyzed Swedish Mammography Cohort data on 61,433 women who completed food frequency questionnaires at enrollment in 1987 to 1990.

In the July issue of the International Journal of Cancer, they report that 2952 incident cases of invasive breast cancer developed during a mean follow-up of 17.4 years. ER and PR status was known in 2062 cases, of which 1286 (62.4%) were ER+/PR+, 417 (20.2%) were ER+/PR-, 266 (12.9%) were ER-/PR-, and 93 (4.5%) were ER-/PR+.

"Glycemic load, but not carbohydrate intake or glycemic index, was significantly positively associated with risk of overall breast cancer," the authors report.

When patients were stratified by ER and PR status, carbohydrate intake, glycemic index and glycemic load were positively associated with risk of ER+/PR- breast cancer.

On multivariate analysis, women in the highest quintile of glycemic index had a 44% increased relative risk (p for trend=0.01) of ER+/PR- breast cancer compared to women in the lowest quintiles. Women in the highest quintile of glycemic load had an 81% increased relative risk for ER+/PR- tumors (p for trend=0.0008), and those in the highest quintile of carbohydrate intake had a 34% increased relative risk (p for trend=0.04), compared to those in the lowest quintiles.

"High-glycemic load diets may increase breast cancer risk via increased concentrations of insulin, insulin-like growth factor-1 and sex hormones," the investigators speculate. Estrogens, insulin and insulin-like growth factor-1 contribute to the proliferation of mammary epithelial cells and estrogen-dependent breast cancer cells, they point out.

"An association between glycemic load and breast cancer risk may be stronger or limited to ER+ tumors," the authors note. At this point, they admit, "We have no explanation for the lack of observed association between glycemic load and risk of ER+/PR+ tumors."

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