Two studies published this week add to a growing body of evidence that some supplements sold to improve health may in fact be killers.
On Tuesday, researchers reported that men who took fairly moderate doses of vitamin E -- 400 international units a day -- had more prostate cancers than men who took a placebo. And a Finnish study published on Monday found that older women who took dietary supplements, including multivitamins, folic acid, iron and copper, appeared to be more likely to die early than women who didn’t.
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Supplement makers have long argued that their products cannot hurt, and that they likely boost health. The Council for Responsible Nutrition, a lobby group for supplement makers, says 150 million Americans take supplements.
Vitamin companies battled for years with the U.S. Food and Drug Administration over regulation and finally triumphed in 1994 with the Dietary Supplement Health and Education Act, which Congress has renewed ever since. It makes the manufacturers -- not the FDA -- responsible for the safety of their products. That means these products are not subject to FDA review.
For the prostate cancer study, researchers reviewed data from a big study in the United States, Puerto Rico, and Canada called SELECT, and found that for every group of 1,000 men, 76 of those given vitamin E supplements got prostate cancer over seven years, compared to 65 similar men who were given a placebo. That’s a 17 percent rise in the risk of prostate cancer over seven years, they reported in the Journal of the American Medical Association.
"Based on these results and the results of large cardiovascular studies using vitamin E, there is no reason for men in the general population to take the dose of vitamin E used in SELECT as the supplements have shown no benefit and some very real risks," Dr. Eric Klein, a physician at the Cleveland Clinic who worked on the study, said in a statement.
The SELECT study was begun in 2001 after a Finnish study found in 1998 that male smokers who took vitamin E had a lower prostate cancer risk.
"SELECT has definitively shown a lack of benefit from vitamin E and selenium supplements in the prevention of prostate cancer and has shown there is the potential for harm," said Dr. Lori Minasian, acting director of NCI's Division of Cancer Prevention, who also worked on the study. "Nevertheless, this type of research has been critically important to understanding the potential benefits and risks from supplements."
In the study involving women, Jaakko Mursu of the University of Eastern Finland and the University of Minnesota and colleagues used data collected during the Iowa Women's Health Study from 38,772 women, whose average age was about 62. More than 62 percent of the women said they took some kind of supplement daily in 1986, but this rose to more than 85 percent in 2004.
Most supplements did little to help these women live any longer than women who didn’t take them, and some appeared to raise the risk of death, Mursu’s team reported.
Multivitamins, vitamin B6, folic acid, iron, magnesium, zinc, and copper were all associated with increased risk of death, while calcium supplements seemed to lower it.
"Based on existing evidence, we see little justification for the general and widespread use of dietary supplements," the researchers wrote in the Archives of Internal Medicine.
The Council for Responsible Nutrition said Mursu’s study was “a hunt for harm.” It did not denounce the prostate study. “Men shouldn’t rush to judgment about vitamin E based on this study, but instead should consider the body of evidence, the amount being taken, and their individual medical history,” said the group’s Duffy MacKay.