Glycemic index, glycemic load, and cancer risk: a meta-analysis1–3

Background: Factors linked to glucose metabolism play an impor-tant role in the development of cancers, and both glycemic index (GI) and glycemic load (GL) have been investigated as potential etiologic factors. Objective: A meta-analysis was performed to explore the associa-tion between GI and GL and cancer risk from published studies. Design: A comprehensive, systematic bibliographic search of the medical literature was conducted to identify relevant studies. Case-control and cohort studies published before October 2007 that re-ported cancer risk estimates for GI and GL were included. Pooled relative risks (RRs) were estimated for breast, colorectal, endome-trial, and pancreatic cancer. Results: Thirty-nine studies were included in the meta-analysis. The interquantile ranges of GL were significantly wider in case-control studies, most of which were conducted in European countries, than in cohort studies. Cohort studies that presented lower ranges of GL also reported lower risk estimates. Overall, both GL and GI were significantly associated with a greater risk of colorectal (summary RR 1.26; 95 % CI: 1.11, 1.44 and RR 1.18; 95 % CI: 1.05, 1.34, respectively) and endometrial (RR 1.36; 95 % CI: 1.14, 1.62 and RR 1.22; 95 % CI: 1.01, 1.49) cancer than of breast and pancreatic cancer. There was, however, a significant between-study heteroge-neity for colorectal cancer (P 0.0001). The association between GL and breast cancer disappeared when publication bias was taken into account. No association was found for pancreatic cancer. Conclusion: This comprehensive meta-analysis of GI and GL and cancer risk suggested an overall direct association with colorectal and endometrial cancer. Am J Clin Nutr 2008;87:1793–801.