CHICAGO -- Men who pop too many vitamins in the hope of improving their health may in fact be raising their risk of the deadliest forms of prostate cancer, especially men with a family history of the disease, researchers said yesterday.
Researchers at the National Cancer Institute found that men who exceeded the recommended dose -- taking more than seven multivitamins a week -- increased the risk of advanced cancer by about 30 percent.
The researchers followed 295,344 men over five years to see if there was a link between multivitamin use and prostate cancer.
"We didn't see any relationship with overall prostate cancer," said Dr. Michael Leitzmann, a National Cancer Institute investigator who worked on the study. He said the increased risk from overuse of multivitamins was linked to more aggressive cancer that has spread beyond the prostate gland or cancer that proved fatal.
In men who took too many multivitamins, the risk of aggressive cancer increased by one third, and the risk of fatal prostate cancer doubled compared to those who took no multivitamins, according to the study, published in the Journal of the National Cancer Institute.
"We only saw the increase among the subgroup of men who used multivitamins in excessive amounts," Leitzmann said in a telephone interview.
The researchers said the association was strongest in men with a family history of prostate cancer and men who also took selenium, beta-carotene, or zinc supplements.
Just over a quarter of a million men will be diagnosed with prostate cancer in the United States this year, but fewer than 30,000 will die of it because the tumors grow slowly.
No studies have yet found that people benefit from taking multivitamin and mineral supplements, and some studies have found that vitamins like A and iron are toxic at high levels. Beta-carotene has been found to increase the risk of lung cancer in smokers.
Leitzmann said the researchers were not able to pinpoint which vitamin or supplement ingredient could be driving the cancer, saying what it does suggest is the need for more study. "It's certainly a red flag," he said.
The important thing, Leitzmann said, was that men should heed the dosage on their vitamin bottle and use as directed.