An ecological study of cancer mortality rates including indices for dietary iron and zinc.

BACKGROUND Dietary iron and zinc affect the risk of cancer, with dietary iron generally correlated with increased risk and dietary zinc with reduced risk. However, zinc supplements have been found correlated with increased risk of cancer. PATIENTS AND METHODS An ecological study was conducted using state-averaged cancer mortality rate data for white Americans for 1970-94 with indices for alcohol consumption, smoking, Hispanic heritage, and urban residence plus dietary factors for four large U.S. regions. RESULTS The dietary zinc index was inversely correlated with 12 types of cancer, whereas the dietary iron index was directly correlated with 10 types of cancer which correlated with both iron directly and zinc inversely were bladder, breast, colon, esophageal, gastric, rectal cancer, and Hodgkin's lymphoma; those inversely with zinc only were laryngeal, nasopharyngeal, oral, skin and vulvar cancer. Solar UVB was inversely correlated with 10 of the 15 types of cancer for which the iron and/or zinc indices had significant correlations, the smoking and urban indices with nine, and the alcohol index with eight. CONCLUSION Although there are mechanisms that explain why zinc should reduce the risk of cancer, whereas iron should increase the risk, these indices may represent the dietary sources of these nutrients, e.g. whole grains for zinc and red meat for iron, and other components of these dietary factors.