Dietary glycemic load and risk of colorectal cancer in the Women's Health Study

Abstract

Although diet is believed to influence colorectal cancer risk, the long-term effects of a diet with a high glycemic load are unclear. The growing recognition that colorectal cancer may be promoted by hyperinsulinemia and insulin resistance suggests that a diet inducing high blood glucose levels and an elevated insulin response may contribute to a metabolic environment conducive to tumor growth. We prospectively followed a cohort of 38 451 women for an average of 7.9 years and identified 174 with incident colorectal cancer. We used baseline dietary intake measurements, assessed with a semiquantitative food-frequency questionnaire, to examine the associations of dietary glycemic load, overall dietary glycemic index, carbohydrate, fiber, nonfiber carbohydrate, sucrose, and fructose with the subsequent development of colorectal cancer. Cox proportional hazards models were used to estimate relative risks (RRs). Dietary glycemic load was statistically significantly associated with an increased risk of colorectal cancer (adjusted RR = 2.85, 95% confidence interval [CI] = 1.40 to 5.80, comparing extreme quintiles of dietary glycemic load; P(trend) =.004) and was associated, although not statistically significantly, with overall glycemic index (corresponding RR = 1.71, 95% CI = 0.98 to 2.98; P(trend) =.04). Total carbohydrate (adjusted RR = 2.41, 95% CI = 1.10 to 5.27, comparing extreme quintiles of carbohydrate; P(trend) =.02), nonfiber carbohydrate (corresponding RR = 2.60, 95% CI = 1.22 to 5.54; P(trend) =.02), and fructose (corresponding RR = 2.09, 95% CI = 1.13 to 3.87; P(trend) =.08) were also statistically significantly associated with increased risk. Thus, our data indicate that a diet with a high dietary glycemic load may increase the risk of colorectal cancer in women.

Figures

Fig. 1

Multivariable-adjusted relative risk of colorectal cancer as a function of glycemic load. Data were fit by using a restricted cubic spline Cox proportional hazards model, adjusted for the same covariates as in Table 2. Glycemic load values above the 95th percentile were deleted to make the graph more stable; knots were placed at the 5th, 25th, 75th, and 95th percentiles of the remaining observations. Dotted lines = 95% confidence intervals; solid line = adjusted relative risk of colorectal cancer as a function of glycemic load.