RESPONSE: Re: Zinc Supplement Use and Risk of Prostate Cancer

Extract

We read with interest the letter by Chang et al. reporting no association between zinc supplement use and the risk of prostate cancer in a Swedish case-control study. By comparison, our results ( 1 ) suggest that high intake of supplemental zinc is associated with an increased risk of advanced prostate cancer. There are several possible explanations for these discrepant findings. The proportion of subjects in our study with zinc supplement exposure was greater than that in the Swedish study. For example, only 2.5% of the base population in the Swedish study reported using zinc supplements, whereas 25% of the subjects in our study reported using zinc supplements. In addition, it is likely that the doses of zinc consumed by subjects in the Swedish study were largely compatible with the recommended dietary allowance of 11 mg/day of zinc for men, an intake level that is not associated with an increase in prostate cancer risk ( 1 ). By comparison, our study included 4374 men whose zinc intake exceeded the current recommended dietary allowance by at least twofold. Furthermore, it is possible that the duration of zinc supplement use is critical for an increase in prostate cancer risk. In our study, 6177 men reported consistent use of zinc supplements for 10 years or longer. Finally, the apparent adverse effect of zinc supplement use that we observed was restricted to cases of advanced prostate cancer.