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Too Much Zinc Ups Prostate Cancer Risk

Excerpt By Ed Edelson, HealthDay

Men who overdose on zinc supplements more than double their risk of prostate cancer, a government study finds.

The researchers looked at 46,974 men who were involved in the Health Professionals Follow-Up study, and the increased risk was seen in those who took more than 100 milligrams a day of zinc supplements or used zinc supplements for more than 10 years.

The report appears in the July 2 issue of the Journal of the National Cancer Institute.

It's an important finding because prostate cancer is the second leading cancer killer for American men, taking 30,000 lives a year. And 30 percent to 40 percent of all men take one supplement or another, says study author Dr. Michael F. Leitzmann, an epidemiological investigator at the National Cancer Institute.

Zinc has long been a target of prostate cancer research because it is found in high concentrations in the prostate, but studies of its effects on malignancy have gotten mixed results. One study released four years ago found an association between daily doses of zinc and a reduced risk of the cancer.

There isn't necessarily a conflict between the two trials, says Dr. Janet Stanford, a research professor of epidemiology at the Fred Hutchinson Cancer Research Center in Seattle and a leader of the earlier study.

"Our study was not designed to assess supplement use," Stanford says. The new study is "intriguing," she says, and "does raise a question about the role of zinc in prostate cancer. But it is not the basis for making decisions."

Leitzmann agrees, noting his results might not conflict with those from the earlier study, in part because the two trials used entirely different methods. The older study asked men with prostate cancer if they had taken zinc supplements and compared their answers with cancer-free men. The new study followed men who started out cancer-free for 14 years, asking about their zinc intake.

The important point is that the risk was concentrated in men who took the largest amounts of zinc for the longest time, Leitzmann says. No increased risk was found in men who took up to 100 milligrams a day. But those who took more than that amount daily were 2.29 times more likely to develop the cancer than those who took less. And the risk was 2.37 times greater for men who took zinc supplements for 10 or more years.

Zinc is known to increase blood levels of insulin-like growth factor and testosterone, both of which are directly related to prostate cancer, Leitzmann says. It's possible malignancy occurs because high levels of zinc increase the growth rate of slow-growing prostate cancers, he says.

Not much is known about modifiable risk factors for prostate cancer, Leitzmann says. The best known risk factors are increasing age, a family history, and race, with blacks at higher risk.

Even with the latest findings, the evidence that avoiding zinc supplementation might reduce prostate cancer risk "overall is not very compelling," Leitzmann says. "This one study cannot conclusively answer that question."

But one obvious implication is that men "should avoid supplements that contain multiple amounts of the recommended dietary amounts," Leitzmann says.

More information

You can get an overview of what is known about prostate cancer from the National Cancer Institute. For more on the risk factors for prostate cancer, go to the Fred Hutchinson Cancer Research Center.


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