Two other studies found a positive association between heme iron and colorectal cancer but it was not statistically significant (35, 37). In a meta-analysis of 5 prospective studies (Fig. 1), we found a significant increase in risk of colorectal cancer of 8% (RR, 1.08; 95% CI, 1.00–1.17) for 1 mg increase in heme iron intake. Regarding
Overall, associations regarding dietary intake of iron and especially heme iron showed to be positive with colorectal and colon cancer risk. Information concerning iron biomarkers showed an unexpected negative association with risk of developing colorectal cancer.
iologic plausibility behind the dietary iron–induced carcinogenesis relies first in the prooxidant role of iron, which may influence colorectal carcinogenesis by forming ROS (1) that can lead to DNA damage. Second, emerging evidence suggests that heme iron may play a more important role in colorectal carcinogenesis than other forms of iron (18, 47). Heme iron catalyzes the formation of N-nitroso compounds and lipid peroxidation end products, which partially explains the promotion effect of red and processed meat on colorectal cancer (18). Bingham and colleagues conducted a human experiment where they exposed male volunteers to high amounts of red meat or heme iron. They found that these individuals produced higher levels of fecal N-nitroso compounds than when exposed to the same amounts of white meat or ferrous iron (48, 49).
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