Increased risk of cancer mortality associated with cadmium exposures in older Americans with low zinc intake.

Cadmium (Cd) exposure has been associated with increased cancer risk, and zinc (Zn) appears to reduce that risk. However, little is known about the combined influence of Cd and Zn on cancer risk. The aim of this study was to examine relationships between Cd exposure, Zn intake, and cancer mortality risks. The analyses used 5204 subjects aged 50 yr or older from the Third National Health and Nutrition Examination Survey (NHANES III, 1988-1994) and the mortality follow-up through December 31, 2006. Cox proportional hazards models were used to test associations. In total, 569 cancer deaths were recorded during an average follow-up of 12.4 yr, including 155 from lung, 61 from prostate, and 26 from breast cancer. A positive association between Cd and cancer mortality risk was identified for both genders. Despite limited cause-specific deaths, the increased risk associated with Cd was significant for lung cancer in men. All-cause cancer mortality risk was significantly elevated among women with Zn intakes below the recommended dietary allowance (RDA) compared with women who met the RDA. The effect of low dietary Zn was not observed in men. Similar trends for prostate and breast cancer deaths were not significant. There was a significant inverse association between cancer deaths and the Zn-to-Cd ratio for both genders. Cd exposure is an important independent risk factor of cancer mortality in older Americans and the risk appears exaggerated in those with inadequate dietary Zn. Additional studies are required to elucidate the mechanism(s) by which Zn participates in the carcinogenic influence of Cd.