Cruciferous vegetable consumption and colorectal cancer risk: Meta-analysis of the epidemiological evidence

A number of studies suggest a protective role of cruciferous vegetables in colon cancer risk. We conducted meta-analyses on the twenty published epidemiological studies which we could identify that contained information on the relationship of consumption of the cabbage or vegetables of the Brassica genus to the incidence of colon or rectal cancer or their precursors. Most of these studies were conducted to examine relationships between fiber and colon cancer, which reduces the risk of publication bias. Differences in the design and exposure assessment among the studies was accounted for in a deductive analysis of alternative hypothesis with general variance-based, homogeneity testing and meta-regression methods. A general protective effect of cruciferous vegetables on colorectal cancer was found. The odds ratio of the meta-analysis equaled 0.94 (95% CI = 0.92, 0.96) for every 4.3 grams/day intake of cruciferae (weighted mean intake of studies). Meta-regression models based on linear regression were used to estimate the effect across reported cruciferae consumption levels and studies. The crude model suggested highly protective effect of cruciferous vegetable and total vegetable on colorectal cancer with OR of 0.91 (CI = 0.90, 0.94) and 0.90 (CI = 0.86, 0.93), respectively, for each 10 gram of consumption per day. The effect was OR=0.91 per 10 gram of cruciferae consumed for colon cancer and 0.95 for rectal cancer (both were significant at α=0.05). To discriminate a cruciferous vegetable effect from the effect of greater consumption of vegetables in general, we modeled the residual cruciferae intake along with the frequency of total vegetable intake. A marginally significant protective effect (p=0.053) remained for the association to colorectal cancer with OR equal to 0.95 (CI=0.91, 1.00) for each 10 grams/day of cruciferae consumed. These findings suggest that even infrequent consumption of cruciferous vegetables provides protection against colon cancer in man.