A role of hyperinsulinemia in the development of colorectal cancer has been postulated and is supported by the idea that insulin-like growth factors can activate the proliferation of cancer cells in the colon. Therefore, determinants of serum-insulin levels like the glycemic load could potentially influence cancer risk. We evaluated whether an elevated glycemic load of the diet is associated with the risk of colorectal cancer in the Netherlands Cohort Study on Diet and Cancer (NLCS). The NLCS was initiated in 1986 and included 120,852 men and women. Participants completed a self-administered semi-quantitative food frequency questionnaire covering dietary habits in the year preceding baseline. The Foster-Powell glycemic index table was used as reference to calculate the glycemic index of the diet, expressed as a percentage of the glycemic response elicited by glucose as standard food. A glycemic index was available for more than 95% of foods. The glycemic index represents the quality of carbohydrate but does not take into account the quantity, therefore, in data-analyses the glycemic load was used. The total daily glycemic load assesses the total glycemic effect of the diet. After 11,3 years of folow-up, 1361 colon and 450 rectal cancer cases were detected. Accumulation of the person time in the cohort was estimated through vital status follow-up of a subcohort of 5,000 men and women who were randomly selected after baseline exposure measurement. Using a case-cohort approach, Cox proportional hazard analysis was used to estimate sex- and cancer site specific hazard ratios (RR) and 95% confidence intervals (CI) for cancer risk according to quintiles of energy adjusted glycemic load. RR were adjusted for age, Body Mass Index, family history of colorectal cancer, smoking, intake of calcium, intake of alcohol, intake of processed meat, educational level and physical activity. Interactions were tested for glycemic load with Body Mass Index, fibers from cereals, fibers from fruit and vegetables, family history of colorectal cancer and diabetes. The mean (SD) glycemic load per day was 136.8 (41.3) g/day for men and 102.7 (29.3) g/day for women. There was no statistically significant association between glycemic load and colon or rectum cancer risk. The RR for colon cancer for the highest versus the lowest quintile of glycemic load was 0.74 (95% CI 0.54-1.02) for men and 1.10 (95% CI 0.78-1.54) for women. For rectum cancer, the RR were 1.03 (95% CI 0.69-1.53) for men and 0.80 (95% CI 0.45-1.43) for women. There were no significant interactions. In conclusion, our findings do not support the hypothesis that a high glycemic load diet is associated with a higher risk of colon and rectal cancer in men and women.
[Fifth AACR International Conference on Frontiers in Cancer Prevention Research, Nov 12-15, 2006]