Processed meat and colorectal cancer: a quantitative review of prospective epidemiologic studies.

A tremendous amount of scientific interest has been generated regarding processed meat consumption and cancer risk. Therefore, to estimate the association between processed meat intake and colorectal cancer (CRC), a meta-analysis of prospective studies was conducted. Twenty-eight prospective studies of processed meat and CRC were identified, of which 20 represented independent nonoverlapping study populations. Summary relative risk estimates (SRREs) for high versus low intake and dose-response relationships were calculated. The SRRE for high (vs. low) processed meat intake and CRC was 1.16 [95% confidence interval (CI): 1.10-1.23] for all studies. Summary associations were modified considerably by sex; the SRRE for men was 1.23 (95% CI: 1.07-1.42) and the SRRE for women was 1.05 (95% CI: 0.94-1.16), based on nine and 13 studies, respectively. Sensitivity analyses did not indicate appreciable statistical variation by tumor site, processed meat groups, or study location. The SRRE for each 30-gram increment of processed meat and CRC was 1.10 (95% CI: 1.05-1.15) based on nine studies, and the SRRE for each incremental serving of processed meat per week was 1.03 (95% CI: 1.01-1.05) based on six studies. Overall, summary associations were weak in magnitude (i.e. most less than 1.20), processed meat definitions and analytical comparisons were highly variable across studies, and isolating the independent effects of processed meat intake is difficult, given the likely influence of confounding by other dietary and lifestyle factors. Therefore, the currently available epidemiologic evidence is not sufficient to support a clear and unequivocal independent positive association between processed meat consumption and CRC.