Specifically, supplements of antioxidants, folic acid and vitamin B seem to hold no benefits, and could potentially even be harmful, though more research is necessary, the editorial's authors said. And beta carotene, vitamin E and possibly high doses of vitamin A may be harmful. Multivitamins also don't seem to hold any additional benefits, they said, writing, "this evidence, combined with biological considerations, suggests that any effect, either beneficial or harmful, is probably small."
Consumers are always looking for ways to minimize their cancer risk, which is one reason why many turn to over-the-counter vitamin and mineral supplements. But new research finds that while companies promote dietary supplements for their cancer-prevention benefit, some may end up doing more harm than good.
Vitamin sales in the U.S. were over $28 billion in 2010, according to the authors, and have steadily risen in the last few decades, despite lacking evidence for their effectiveness in chronic disease prevention. About half of Americans take some sort of vitamin or supplement, and it’s unlikely that multivitamins are going to go away overnight.
Dr. Tim Byers, MD/MPH, says consumers should be cautious about using supplements. However, this doesn't mean you have to avoid them altogether. "I think when people take supplements they shouldn't take them at levels higher than what you can get in your diet," he said. Byers and other experts urge people to incorporate more fruits and vegetables into their diet, rather than relying on supplements.
A person who has a known deficiency of a certain vitamin or mineral -- either due to diet or health condition that prevents proper absorption -- can take a supplement, preferably a multivitamin that provides levels in line with recommended daily allowances. But in every case, Byers cautions consumers to acknowledge that there may be "harm in excess."
The Centers for Disease Control and Prevention also recommends that pregnant women take 400 micrograms daily of folic acid to prevent birth defects such as spina bifida.
“Sales of multivitamins and other supplements have not been affected by major studies with null results, and the U.S. supplement industry continues to grow, reaching $28 billion in annual sales in 2010,” wrote the authors of the editorial summary, led by Dr. Eliseo Guallar, a professor of epidemiology who specializes in heart disease prevention at Johns Hopkins Bloomberg School of Public Health in Baltimore. “We should translate null and negative findings into action. The message is simple: Most supplements do not prevent chronic disease or death, their use is not justified, and they should be avoided.”
The first study, which was released online Nov. 12 in Annals, was a review of 24 studies and two trials on more than 350,000 individuals that looked at vitamin supplementation’s role in preventing chronic disease. The review was conducted to find evidence that can be used to update vitamin treatment guidelines from the U.S. Preventive Services Task Force, a panel of medical experts who recommend the government on treatments.
That review found no evidence that vitamin and mineral supplementation would reduce heart disease in pill takers. Two of the trials found a small, “borderline-significant benefit” in cancer risk reduction, but only in men. Overall, the panel concluded there was no solid evidence for or against taking vitamins and minerals alone, or that a multivitamin to prevent heart disease or cancer. More strikingly, it found enough evidence to recommend against taking beta-carotene or vitamin E for preventing both diseases, finding they not only didn’t help but the former may raise risk for lung cancer for already at-risk individuals.
“In the absence of clear evidence about the impact of most vitamins and multivitamins on cardiovascular disease and cancer, health care professionals should counsel their patients to eat a healthy, well-balanced diet that is rich in nutrients,” the Task Force concluded.
The next study, published Dec. 16 in Annals, looked at cognitive health and whether long-term use of multivitamins would have any effect. Researchers assigned almost 5,950 male doctors aged 65 and older to take either a daily multivitamin or placebo for 12 years in a randomized, placebo-controlled trial,
Based on the results of memory tests, the researchers found the multivitamin did nothing to slow cognitive decline among men 65 and older compared to placebo takers.
“These data do not provide support for use of multivitamin supplements in the prevention of cognitive decline,” wrote the authors, led by Dr. Francine Grodstein, an epidemiologist who studies aging at Harvard School of Public Health in Boston.
It’s worth noting this study only looked at cognitive test results, not actual development of dementia.
Heart Attack and Stroke
The third study looked specifically at multivitamins and minerals role in preventing another heart attack, or myocardial infarction. They looked at more than 1,700 people who had a heart attack at least six weeks earlier, and randomized them to receive daily high-dose multivitamins and minerals or placebos for five years.
Having a heart attack raises risk for another attack, or cardiovascular event like stroke or premature death, so if multivitamins could reduce risk, they could be a boon to public health.
The researchers found no difference in rates of another heart attack, chest pain, the need for hospitalization, cardiac catheterization, or rates of stroke and early death between vitamin-takers and placebo-takers. But, they said the conclusions should be taken with caution, because several participants stopped taking vitamins early.
The authors of the editorial say the evidence is clear about multivitamin supplements, except for vitamin D, which has been shown to be both effective and ineffective for preventing falls and fractures in elderly. More studies are needed specifically looking at vitamin D, according to the editorial's authors.
Dr. Tim Byers, director for cancer prevention and control at the University of Colorado Cancer Center, conducted a meta-analysis of two decades worth of research -- 12 trials that involved more than 300,000 people -- and found a number of supplements actually made a person much more likely to develop certain types of cancer.
Byers began his investigation on the association between supplements and cancer risk 20 years ago. He and many other researchers observed that people who ate more fruits and vegetables cut their risk for cancer. Byers and his colleagues wondered if taking supplements that provide the same vitamins and minerals as fruits and vegetables could offer similar protection.
But his findings suggested just the opposite -- rather than warding off cancer, taking lots of supplements may raise a person's risk.
"There's enough evidence along these lines that we should really consider better regulation of these nutritional supplements," Byers told CBS News. "I think it's time to step back and say there's probably a safety issue."
Byers presented his research Monday at the annual meeting of the American Association for Cancer Research, in Philadelphia.
"Through his analysis, Byers found that people who took high doses beta carotene supplements had an increased risk for lung cancer. Selenium supplements were associated with skin cancer. Men who took vitamin E had an elevated risk for prostate cancer. Folic acid, a B vitamin, taken in excess could lead to an increased risk for colon cancer."
Byers says it's still unclear why supplements could have this adverse effect, but he and other researchers hope to learn more about the association.
“There is now evidence that high doses of some supplements increase cancer risk," writes Byers. "Despite this evidence, marketing claims by the supplement industry continue to imply anticancer benefits. Insufficient government regulation of the marketing of dietary supplement products may continue to result in unsound advice to consumers. Both the scientific community and government regulators need to provide clear guidance to the public about the use of dietary supplements to lower cancer risk.”
“This is an extremely striking observation, but not surprising given the rather disappointing outcomes of patients at risk for developing lung cancer who had been treated with various antioxidants,” David Tuveson of Cold Spring Harbor Laboratory who was not involved in the work, told The Scientist at the time. “We should now consider whether people consuming high doses of antioxidants are ironically promoting cancers that they seek to prevent.”
Other studies Byers reviewed indicated that many other supplements had no apparent impact on cancer risk -- neither increasing nor decreasing it. Recent research has shown that for the most part, vitamin supplements have little impact on a person's long-term health. Some research has even gone as far as to say that they are a waste of money.
In women aged 55 to 69 years, several widely used dietary vitamin and mineral supplements, especially supplemental iron, may be associated with increased risk for death, according to new findings from the Iowa Women's Health Study.
Jaakko Mursu, PhD, from the Department of Health Sciences, Institute of Public Health and Clinical Nutrition at the University of Eastern Finland in Kuopio, Finland, and colleagues reported their findings in the October 10 issue of the Archives of Internal Medicine.
"In agreement with our hypothesis, most of the supplements studied were not associated with a reduced total mortality rate in older women," Dr. Mursu and colleagues conclude. "In contrast, we found that several commonly used dietary vitamin and mineral supplements, including multivitamins, vitamins B6, and folic acid, as well as minerals iron, magnesium, zinc, and copper, were associated with a higher risk of total mortality."
"Although we cannot rule out benefits of supplements, such as improved quality of life, our study raises a concern regarding their long-term safety," the authors add.
Evidence involving tens of thousands of people randomly assigned in many clinical trials shows that β-carotene, vitamin E, and possibly high doses of vitamin A supplements increase mortality and that other antioxidants, folic acid and B vitamins, and multivitamin supplements have no clear benefit.
The large body of accumulated evidence has important public health and clinical implications. Evidence is sufficient to advise against routine supplementation, and we should translate null and negative findings into action. The message is simple: Most supplements do not prevent chronic disease or death, their use is not justified, and they should be avoided. This message is especially true for the general population with no clear evidence of micronutrient deficiencies, who represent most supplement users in the United States and in other countries.
The evidence also has implications for research. Antioxidants, folic acid, and B vitamins are harmful or ineffective for chronic disease prevention, and further large prevention trials are no longer justified. Vitamin D supplementation, however, is an open area of investigation, particularly in deficient persons. Clinical trials have been equivocal and sometimes contradictory. For example, supplemental vitamin D, which might prevent falls in older persons, reduced the risk for falls in a few trials, had no effect in most trials, and increased falls in 1 trial. Although future studies are needed to clarify the appropriate use of vitamin D supplementation, current widespread use is not based on solid evidence that benefits outweigh harms.
With respect to multivitamins, the studies published in this issue and previous trials indicate no substantial health benefit. This evidence, combined with biological considerations, suggests that any effect, either beneficial or harmful, is probably small. As we learned from voluminous trial data on vitamin E, however, clinical trials are not well-suited to identify very small effects, and future trials of multivitamins for chronic disease prevention in well-nourished populations are likely to be futile.
"Regulation of supplements in the U.S. has long been under fire for being too lax; critics note that while the Dietary Supplement and Health Education Act (DSHEA) doesn't allow supplements to be marketed as being able to cure disease, it makes it easy for a company to sell products with very little oversight. Since DSHEA was passed in 1994, the estimated number of supplement products rose from 4,000 to more than 55,000 in 2012, the CDC researchers said, amounting to some $15 billion spent each year on herbal or complementary nutritional products.
Products don't need FDA approval to come to market, and companies are only required to report serious adverse events to the agency. The FDA can ask manufacturers to recall their products, which the agency has done more than 200 times from 2004 to 2012, when supplements were found to contain unlabeled ingredients.
"...Investigators tested 24 supplements claiming to be seven different types of herb — echinacea, garlic, gingko biloba, ginseng, saw palmetto, St. John’s wort and valerian root. All but five of the products contained DNA that was either unrecognizable or from a plant other than what the product claimed to be."
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