Two new studies published this week in journals of the American Medical Association have found evidence that taking extra doses of vitamin supplements may significantly increase risks to health and longevity.
“There really is not any compelling evidence that taking these dietary supplements above and beyond a normal dietary intake is helpful in any way, and this is evidence that it could be harmful,” said Dr. Eric Klein of the Cleveland Clinic, principal author of one of the new studies.
One study, published today in JAMA, the journal of the American Medical Association, found that use of a Vitamin E supplement (400 IU daily) significantly increased the risk of prostate cancer among healthy men. The second and separate study, published in the October 10 issue of the Archives of Internal Medicine, a journal of the American Medical Association, found that older women who used multivitamins and certain other vitamin supplements had an increased risk of dying over a 19-year follow-up period, compared to women who did not use the supplements.
The Vitamin E and Prostate Cancer Study
The first of these studies, conducted by Dr. Eric Klein of the Department of Urology, Glickman Urological and Kidney Institute at the Cleveland Clinic in Cleveland, Ohio, and colleagues, was published today in JAMA, the journal of the American Medical Association.
The study, known as the Selenium and Vitamin E Cancer Prevention Trial, or Select trial, included 35,533 men in a trial started in 2001 to determine whether vitamin E or selenium, either alone or in combination, could lower a man’s risk for prostate cancer. The men were randomly assigned to four groups: (1) men who were assigned to take a daily supplement of 400 IU of vitamin E plus a selenium placebo, (2) men who were assigned to take a daily supplement of 200 micrograms of selenium plus a vitamin E placebo, (3) men who were assigned to a daily supplement of 400 IU of vitamin E plus a daily supplement of 200 micrograms of selenium, and (4) a control group who were assigned to take two placebos.
All of the men were free of prostate cancer when they started the trial at age 50 years or older for black men and 55 years or older for all others.
The trial was terminated in 2008, because a preliminary review of the data showed no benefit from the supplements, but suggested what then appeared to be an insignificant increase in the risk of prostate cancer and diabetes among study participants taking the supplements.
The current study report includes additional data, based on a longer follow-up of the men in the trial, through July 5, 2011. The additional follow-up data showed that in fact users of vitamin E (only) had a statistically significant 17 percent higher risk of prostate cancer than the men in the control group who did not take any supplements. Those who took only the selenium had a 9 percent higher risk of prostate cancer, and those who took both the vitamin E and the selenium supplements had a 5 percent higher risk of prostate cancer, compared with the men in the control group. The study found no increased risk of diabetes.
The researchers deemed the vitamin E result to be significant. “Dietary supplementation with vitamin E significantly increased the risk of prostate cancer among healthy men,” they concluded.
The Iowa Study of Vitamin Supplements and Mortality in Older Women
The other new study, by Jaakko Mursu, PhD of Institute of Public Health and Clinical Nutrition, University of Eastern Finland, and colleagues from the University of Minnesota and the University of Oslo, was published in the October 10 issue of the Archives of Internal Medicine, a journal of the American Medical Association.
The researchers analyzed data from the Iowa Women’s Health Study which assessed the use of vitamin and mineral supplements in relation to total mortality in 38,772 older women. The women, who were on average 61.6 years old, self-reported their use of vitamin supplements at the beginning of the study in 1986, and at follow-ups in 1986, 1997, and 2004.
Through December 31, 2008, a total of 15,594 (40.2%) of the women had died.
Applying statistical analysis, the researchers found that use of multivitamins and other dietary supplements increased the risk of death by the following percentages, compared to nonuse: multivitamins (absolute risk increase, 2.4%), vitamin B6 (4.1%), folic acid (5.9%), iron (3.9%), magnesium (3.6%), zinc (3.0%), and copper (18.0%) . “Findings for iron and calcium were replicated in separate, shorter-term analyses (10-year, 6-year, and 4-year follow-up), each with approximately 15% of the original participants having died, starting in 1986, 1997, and 2004,” the researchers wrote.
Unlike other studies, this study found that use of calcium reduced the risk of dying among the study participants by an absolute risk reduction of 3.8%.
The researchers reported, “In older women, several commonly used dietary vitamin and mineral supplements may be associated with increased total mortality risk; this association is strongest with supplemental iron. In contrast to the findings of many studies, calcium is associated with decreased risk.”
“Based on existing evidence, we see little justification for the general and widespread use of dietary supplements,” the authors concluded.
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