October 12, 2011
Prolonged Use Of Vitamin E Ups Prostate Cancer Risk
New evidence that taking vitamin E supplements can be risky to your health adds to the concerns that doctors have that many people may be overusing vitamins and other supplements.
A new study that followed up on men who took high doses of vitamin E for around five years found they had a slightly increased risk of developing prostate cancer -- even after they had stopped taking the pills.
“If you have enough of these vitamins in your system... extra doesn´t help you any, and too much of something like this can be harmful,” study author Dr. Eric Klein, from the Cleveland Clinic, told Reuters Health reporter Genevra Pittman.
“People tend to think of vitamins as innocuous substances, almost like chicken soup – take a little and it can´t hurt,” Klein told Lyndsey Tanner of the Associated Press (AP). The study shows this is not true. “If you have normal levels, the vitamin is probably of no benefit, and if you take too much, you can be harmed.”
The findings follow another recent study that suggests taking too many vitamins and supplements increases a woman´s risk of having a stroke. “There's a theme here that taking vitamins is not only not helpful but could be harmful” in people who aren´t deficient, Klein told Reuters.
Klein and his colleagues examined the long-term effect of vitamin E and selenium on risk of prostate cancer in relatively healthy men. The study, SELECT, included 35,533 men from 427 study sites in the US, Canada and Puerto Rico between August 2001 and June 2004.
Eligibility criteria included a prostate-specific antigen (PSA) measure below a certain level, a digital rectal exam not suspicious for prostate cancer, and age 50 or older for black men and 55 or older for other men.
The primary analysis included 34,887 men who were randomly assigned to 1 of 4 treatment groups: 8,752 received 200mg selenium per day; 8,737 received 400 IU/day vitamin E; 8,702 received both; and 8,696 received a placebo. The men were scheduled to a planned follow-up between a minimum of 7 years and a maximum of 12 years.
Since the initial report, a total of 521 additional prostate cancers have been diagnosed: 113 in the placebo group, 147 in the vitamin E group, 143 in the selenium group, and 118 in the combo group. The researchers found that the rate of prostate cancer detection was greater in all treatment groups when compared with the placebo group, but was statistically significant only in the vitamin E alone group.
In all, 529 men in the placebo group developed prostate cancer, 620 men in the vitamin E group developed the cancer, 575 in the selenium group and 555 in the combo group. The difference in rates of prostate cancer between the vitamin E and placebo group became evident during the participants´ third year in the trial.
The researchers calculated that men in the 400 IU/day vitamin E group were 17 percent more likely to get prostate cancer than those in the placebo group. That dose, commonly found in over-the-counter supplements, is nearly 20 times higher than the recommended daily amount for adults.
The results mean that for every 1,000 men who took vitamin E, there were 11 additional cases of prostate cancer, compared with men taking placebos. Experts say about 160 out of every 1,000 US men will develop prostate cancer in their lifetime. And the National Cancer Institute says about 241,000 men in the US will be diagnosed with prostate cancer in 2011, and close to 34,000 will die from it.
The study was halted in 2008 when the researchers noticed the increased risk of prostate cancer in men taking vitamin E, but they continued to monitor them for cancer after they stopped taking the supplements. And the researchers found that the extra risk became clearer over time.
By mid-2011, about seven percent of men who had taken vitamin E only had gotten prostate cancer, compared to six percent of those assigned to the placebo pills.
The researchers didn't find an extra risk of prostate cancer in men who took only selenium or vitamin E together with selenium.
Klein said it´s not clear how vitamin E would increase the risk of prostate cancer, and that not all past studies have shown it does any harm at all. Some have even shown a lower prostate cancer risk with vitamin E usage.
The new findings are not definitive proof that vitamin E is the culprit of extra prostate cancers, but that there was not anything else that could explain why men taking the supplement were more likely to be diagnosed with the disease.
Prostate cancer researcher Dr. Neil Fleshner, from the University of Toronto, was doubtful that vitamin E increases the risk of prostate cancer, and said the result may have been a chance finding, or a “false positive.”
“It´s an interesting finding. I´m not sure I believe it,” Fleshner told Reuters Health. Either way, vitamin E doesn´t seem to be beneficial for prostate health. “There´s certainly no major evidence that vitamin E helps “¦ So, why bother?” he said.
Still, about 13 percent of American men continue to take vitamin E, according to a supplement trade group.
Men should stop taking large doses and talk to their physicians about the risks and benefits from prostate cancer screening, said Dr. Otis Brawley, chief medical officer for the American Cancer Society. Smaller doses are probably fine, said Brawley, who was not involved in the research.
Other than through supplementation, vitamin E can be found in nuts, seeds and vegetable oils. It helps nerves, muscles, blood vessels and the immune system function. Vitamin E supplements have long been promoted for disease prevention, but research has proven that many claims are false and has suggested they might actually increase risks for some conditions, including heart failure.
“There should be a global warning that ... excessive use of vitamins has not been proven to be beneficial and may be the opposite,” Brawley told the AP.
Experts generally agree that foods are the best sources for vitamins.
Duffy MacKay of the Council for Responsible Nutrition, a supplement makers´ trade group, said the study shouldn´t be interpreted as questioning the benefits of vitamin E as an essential nutrient, and he said there is evidence that many Americans don´t get enough.
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