Whole grain intake and cancer: An expanded review and meta analysis

Whole grains are nutrient-rich and may protect against chronic disease. We previously reviewed 14 case-control studies of colorectal, gastric and endometrial cancers and found consistently lower risk for high versus low whole grain intake. Questions remained concerning other cancers, dietary assessment, quantity consumed, confounding, and differential study quality. Here we expand the review to 40 case-control studies of 20 cancers and colon polyps. Odds ratios were < 1 for 46 of 51 mentions. The pooled odds ratio for high versus low whole grain intake was 0.69 (95% Cl: 0.61, 0.77); consistent across 4 types of dietary questionnaires. Odds ratios were < 1 in 10/13 mentions of studies of colorectal cancers and polyps, 7/8 mentions of gastric and 7/7 of other digestive tract cancers, 7/7 mentions of hormone-related cancers, 4/4 mentions of pancreatic cancer, and 11/12 for 8 other cancers. Most pooled odds ratios for specific cancers were in the range 0.5 - 0.8, notable exceptions being breast (0.86) and prostate (0.90). The pooled odds ratio was similar in studies which adjusted for few or many covariates. Dose-response associations were seen, weakest in studies which used the most detailed questionnaires. A reporting bias is unlikely to explain these results. Any tendency for cases to overreport whole grain intake would bring the observed odds ratio closer to 1. The case-control evidence is supportive of the hypothesis that whole grain intake protects against various cancers.