Heme iron from beef and its role in colon carcinogenesis
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Red meat is an important dietary source of iron compared to other animal products (Table 1). Animal products contribute about 28% of the total iron to the food supply (National Research Council, 1988) Iron is an essential metal in mammals for oxygen and cart>on dioxide transport by hemoglobin and for the function of many enzymes, including catalase and cytochromes Iron also is required for the growth of all living cells, including tumor cells. In fact, the role of iron in cell proliferation is thought to represent an important factor in the clonal expansion of cancer cells. Studies have shown that transferrin, the major serum iron binding protein, is one of the essential substances required for the growth of cells in serum free media (Hann et al., 1988). Results of some studies have been consistent with the hypothesis that increased body iron stores are associated with an increased risk of cancer (Stevens et al, 1986; Selby and Friedman, 1988). Stevens et al. (1988) stated that iron may influence the risk for some cancer sites, including colon, bladder and lung Kapsokefalou and Miller (1993) stated that the interaction of lean beef and beef fat enhances nonheme iron absorption in rats. Cermak et al (1993) reported that chronic exposure of tumor cells to iron may, by induction of the intracellular iron scavenger, ferritin, contribute to the resistance of various tumors to oxidant-producing immune effector cells that require iron for their cytotoxic effect. Some studies show that dietary iron enhances the tumor rate in DMH-induced (1,2-dimethylhydrazine dihydrochloride) colon carcinogenesis in mice (Siegers et al, 1988). However, the role of heme iron from beef in colon carcinogenesis still is not clear. The objective of this study was to investigate the effects of beef as a dietary iron source and its contribution to colon carcinogenesis.