July 1, 2003 -- Men who take too many zinc supplements may be increasing their risk of advanced prostate cancer. A new study shows that men who consumed more than 100 mg per day of the mineral were more than twice as likely to develop advanced prostate cancer than those who don't take zinc supplements.
According to researchers, about 15% of the U.S. population uses dietary supplements that contain zinc. About 10% of men who take the supplements have an average daily zinc intake that is 2-3 times higher than the recommended daily allowance of 11 mg per day. Dietary sources of zinc include beef, breakfast cereals, and seafood.
Researchers say zinc is found in higher concentrations in the prostate than in any other soft tissue in the body, but previous studies on zinc and prostate cancer risk have produced conflicting results. Some have suggested that zinc suppresses prostate cancer cell growth, while others say high zinc levels may increase prostate cancer risk.
In this study, researchers used information from the Health Professionals Follow-Up study of 46,974 men from 1986 to 2001 to examine the link between zinc supplements and prostate cancer risk.
Their results appear in the Journal of the National Cancer Institute.
Risk More Than Doubles
Researchers found that although taking zinc supplements of up to 100 mg per day did not increase men's overall risk of prostate cancer, men who took more than 100 mg of supplemental zinc per day were more than twice as likely to develop advanced prostate cancer than nonusers.
Men who took zinc supplements for 10 or more years also were more than twice as likely to have advanced prostate cancer compared with those who didn't take zinc supplements.
Researchers say they can't rule out the fact that some other factor may account for the increase in advanced prostate cancer risk associated with excessive zinc supplementation found by the study. For example, heavy zinc users may have also taken high levels of other supplements that might affect the prostate, such as calcium.
In addition, because zinc has been associated with prostate health, some users may have been self-medicating longstanding prostate cancer symptoms or delayed medical care, which may have increased the risk of the cancer being found at a later, more advanced stage. But researchers say that's unlikely because taking the men's history of prostate cancer screening and early years of follow-up into account didn't alter their findings.
Researcher Michael F. Leitzmann, MD, of the National Cancer Institute, and colleagues say it's not clear how zinc may act in the body to increase prostate cancer risk, but more research to investigate this link between overuse of zinc supplements and advanced prostate cancer is needed.