Subsite-specific dietary risk factors for colorectal cancer: a review of cohort studies

Abstract

Objective. A shift in the total incidence from left- to right-sided colon cancer has been reported and raises the question as to whether lifestyle risk factors are responsible for the changing subsite distribution of colon cancer. The present study provides a review of the subsite-specific risk estimates for the dietary components presently regarded as convincing or probable risk factors for colorectal cancer: red meat, processed meat, fiber, garlic, milk, calcium, and alcohol. Methods. Studies were identified by searching PubMed through October 8, 2012 and by reviewing reference lists. Thirty-two prospective cohort studies are included, and the estimates are compared by sex for each risk factor. Results. For alcohol, there seems to be a stronger association with rectal cancer than with colon cancer, and for meat a somewhat stronger association with distal colon and rectal cancer, relative to proximal colon cancer. For fiber, milk, and calcium, there were only minor differences in relative risk across subsites. No statement could be given regarding garlic. Overall, many of the subsite-specific risk estimates were nonsignificant, irrespective of exposure. Conclusion. For some dietary components the associations with risk of cancer of the rectum and distal colon appear stronger than for proximal colon, but not for all.

Figure 1

Flow diagram of the study selection.

Figure 2

Estimates of relative risk with 95% CI for the highest versus the lowest exposure categories of red meat. (The results are stratified on sex. Open circles: both gender combined. Closed black circles: females. Closed grey circles: men. All estimates are sorted from the lowest to the highest by subsite and sex.)

Figure 3

Estimates of relative risk with 95% CI for the highest versus the lowest exposure categories of processed meat. (The results are stratified on sex. Open circles: both gender combined. Closed black circles: females. All estimates are sorted from the lowest to the highest by subsite and sex.)

Figure 4

Estimates of relative risk with 95% CI for the highest versus the lowest exposure categories of fiber and whole grain. (The results are stratified on sex. Open circles: both gender combined. Closed black circles: females. Closed grey circles: men. All estimates are sorted from the lowest to the highest by subsite and sex.)

Figure 5

Estimates of relative risk with 95% CI for the highest versus the lowest exposure categories of garlic. (Closed black circles: females.)

Figure 6

Estimates of relative risk with 95% CI for the highest versus the lowest exposure categories of milk. (The results are stratified on sex. Closed black circles: females. Closed grey circles: men. All estimates are sorted from the the lowest to the highest by subsite and sex.)

Figure 7

Estimates of relative risk with 95% CI for the highest versus the lowest exposure categories of calcium. (The results are stratified on sex. Open circles: both gender combined. Closed black circles: females. Closed grey circles: men. All estimates are sorted from the lowest to the highest by subsite and sex, except Stemmermann et al. [28].)

Figure 8

Estimates of relative risk with 95% CI for the highest versus the lowest exposure categories of alcohol. (The results are stratified on sex. Open circles: both gender combined. Closed black circles: females. Closed grey circles: men. All estimates are sorted from the lowest to the highest by subsite and sex.)