| Too Much Zinc Ups Prostate Cancer Risk
Men who overdose on zinc supplements
more than double their risk of prostate cancer, a government study
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
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.
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.
Reference Source 101