Ask the Doctor – October 2008
Question for Dr. Rona
Dear Dr. Rona,
I have been using zinc supplements for years and always believed I was doing the right thing. Yesterday on the internet I came across a number of articles referencing a 2003 study from the NCI which stated men who took zinc supplements in dosages of over 100 mgs. a day and men who took zinc supplements for over 10 years had double the risk of prostate cancer than those who took no zinc supplements. It is not clear to me though what dosage was used in those who used zinc for over 10 years.
I had never heard of this and am concerned. I am 60 and in great health. I have taken zinc supplements for approximately 30 years and for about the last 10 years have used 100 mgs. a day divided into 2 dosages of 50 mgs. each with an extra 10 mgs. in a prostate supplement by Brad King called Ultimate Prostate.
I work part time in a health food store and have always recommended supplemental zinc so now I want to be sure whether to continue doing this or not in addition to my own personal concern.
I am very interested to learn what you have to say on this matter. I know many vitamin studies are misleading yet even Dr. Joseph Mercola on his website, www.drmercola.com references this study and he is a naturally oriented Osteopath.
What do you suggest Dr. Rona? Do I stop all zinc supplementation or just ingest the amount (10mgs.) in the Ultimate Prostate formula or follow some other course of action? Do I continue recommending zinc to my customers?
Dr. Rona’s Response
Thank you very much for your excellent questions. The idea that high zinc supplementation is linked to prostate cancer is unproven. The evidence for this association is flimsy, at best, and the connection can probably be explained by the cadmium content of most zinc supplements. There are, in fact, numerous studies indicating that zinc supplementation prevents prostate cancer.
Research indicates that many of the zinc supplements sold at health food stores contain cadmium, a toxic heavy metal. There are also many studies that indicate a relationship between the ingestion of cadmium and the development of prostate cancer.
The reason for the presence of cadmium in zinc supplements appears to be related to the fact that many high sources of zinc in nature are also high cadmium sources and the supplement companies may not be accounting for that factor. The higher the zinc dosage is, the higher the cadmium content.
You can get a very good idea of your body’s storage of both zinc and cadmium by getting a hair mineral analysis done. If either mineral is out of balance, a simple adjustment of your supplement dosages can be made. That’s something you can recommend for all your customers concerned about high dose zinc supplements.
You could continue with your zinc supplements only if you are certain that your supplement brand contains no cadmium. You can do that by calling the manufacturer and getting a printout of the contents of the tablet or capsule in question. In Canada, companies that can be trusted to deliver exactly what’s on the label and nothing else include Natural Factors, AOR (Advanced Orthomolecular Research), Cyto-Matrix and Thorne Research. Be wary of any “whole food” zinc supplements as these most assuredly contain cadmium and other contaminants.
Zoltan P. Rona, M.D., M.Sc.
Leitzmann MF, Stampfer MJ, Wu K, et al. Zinc Supplement Use and Risk of Prostate Cancer. Journal of the National Cancer Institute 2003;95:1004-1007.
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