Vitamins: Research Shows No Benefit and Some Risks
Posted by medconsumers on December 1, 2008
Vitamins Don’t Work: Research Continues to Find No Benefit and Some Risks
Looking for ways to save money? Stop taking vitamins. The scientific case against them has been building over the last few years, starting with the report from the 2006 U.S. National Institutes of Health State-of-the Science Conference on Multivitamins/Mineral Supplements. The next year, a Cochrane review of all antioxidant trials caused an uproar because it found no preventive benefit to taking these supplements and a slight increase in mortality. And just in the last month alone, one new trial found no cancer preventive benefit to taking B vitamins; and another trial found no cardiovascular preventive effects for vitamins C and E. Both were published in the Journal of the American Medical Association.
The B vitamins trial was led by Shumin M. Zhang, MD, and colleagues at Brigham and Women’s Hospital in Boston and Harvard Medical School. The impetus for this trial, explained the researchers, was the prevailing idea that folate, vitamin B6 and vitamin B12 might play an important role in cancer prevention. Yet the researchers also noted that information from earlier trials of folic acid alone or in combination with B vitamins have produced mixed results, and one trial “even raised concerns about deleterious effects.” What’s more, women were underrepresented in these trials.
Zhang and colleagues recruited 5,442 female health professionals, aged 42 years or older with cardiovascular disease or three or more risk factors for heart disease. All were randomly assigned to take a placebo or a daily supplement that combined 2.5 mg of folic acid, 50 mg of vitamin B6 and 1 mg of vitamin B12.
After seven years, the women taking the combination supplement had the same rate of cancer as those taking a placebo. This trial was funded by a grant from the U.S. National Institutes of Health.
Vitamins E and C
The other new trial found that vitamins E and C did not prevent cardiovascular disease in healthy men, aged 50 and older. The Physicians’ Health Study II involved 14,641 male physicians, 5% of whom had cardiovascular disease at the start of the trial. The men were randomly assigned to take 400 IU of vitamin E every other day and 500 mg of vitamin C daily or a placebo.
After a mean follow-up of eight years, the supplements had not reduced the risk for heart attack, stroke, death, heart failure, angina or the need for a coronary artery-opening procedure. Worse, vitamin E was associated with an increased risk for hemorrhagic stroke, or bleeding in brain (39 hemorrhagic strokes in the men taking vitamin E, compared with 23 in those taking a placebo). The negative results shown for vitamin E confirm those from earlier studies that involved men and women with preexisting cardiovascular disease.
This trial was led by Howard D. Sesso, ScD, Harvard School of Public Health, and funded by grants from the National Institutes of Health, the BASF Corporation, Wyeth Pharmaceuticals, and DSM Nutritional Products Inc (formerly Roche Vitamins).
Earlier Vitamin Research:
These two new trials are but a small part of the research that has found vitamins do not prevent illness or prolong life. Far more extensive is the following government report about multivitamins and the Cochrane review of antioxidant trials mentioned at the beginning of this article.
The report from the 2006 NIH State of the Science Conference on Multivitamins/Minerals for the Prevention of Chronic Conditions. A panel of experts was charged with the task of reviewing all placebo-controlled trials designed to see whether multivitamins and/or minerals can prevent cancer; age-related sensory loss; and cardiovascular, endocrine, neurologic, musculoskeletal, gastroenterologic, renal and pulmonary diseases. This is the report’s conclusion:
In systematically evaluating the effectiveness and safety of multivitamins and/or minerals in relation to chronic disease prevention, we found few rigorous studies on which to base clear conclusions and recommendations. Most of the studies we examined do not provide strong evidence for beneficial health-related effects of supplements taken singly, in pairs, or in combinations of 3 or more.
Within some studies or subgroups of the study populations, there is encouraging evidence of health benefits, such as increased bone mineral density and decreased fractures in postmenopausal women who use calcium and vitamin D supplements. However, several other studies also provide disturbing evidence of risk, such as increased lung cancer risk with beta-carotene use among smokers.”
The updated 2008 Cochrane review: “Antioxidant supplements for prevention of mortality in healthy participants and patients with various diseases.” The 68 placebo-controlled trials included in this review attempted to answer these questions: Can antioxidants prevent disease in healthy people? Can they prevent recurrences in people with cancer, heart disease or other illnesses?
This is the Cochrane review’s conclusion:
We found no evidence to support antioxidant supplements for primary or secondary prevention. Vitamin A, beta-carotene, and vitamin E may increase mortality. Future randomized trials could evaluate the potential effects of vitamin C and selenium for primary and secondary prevention. Such trials should be closely monitored for potential harmful effects. Antioxidant supplements need to be considered medicinal products and should undergo sufficient evaluation before marketing.
Funding Questioned: When this Cochrane Review was first published in 2007, we reported its findings and addressed one of the strongest criticisms leveled against it. Many suspected that the review was funded by the pharmaceutical industry to counteract public enthusiasm for vitamins. In our 2007 article on this topic, one of the review’s co-authors was asked about the funding: Christian Gluud, MD, of the Cochrane Hepato-Biliary Group, Rigshospitalet, Copenhagen University Hospital, responded, “The sole sponsor of this review is the Copenhagen University Trial Unit, a publicly funded, not-for-profit clinical research center, and about 90% of the trials in this review were funded by companies that make vitamins.”
Maryann Napoli, Center for Medical Consumers©