New Study Questions Benefit of Antioxidants in Preventing Heart Disease: Opinion
Supplementation with vitamin E, beta-carotene, or both does not appear to prevent heart attacks or strokes, according to a new study in Lancet (2003;361:2017–23). The authors suggest that taking beta-carotene may actually increase the risk of having a heart attack and dying. The new study is the latest of several reports that cast doubt as to whether antioxidants help prevent heart disease and stroke.
In the new study, the results from 15 previously published controlled trials were pooled, using a technique called meta-analysis. Meta-analyses are based on the premise that combining the results of many studies allows one to draw more definitive conclusions. Each of the 15 studies in this analysis had assessed the effectiveness of supplemental vitamin E or beta-carotene in preventing heart disease and death from all causes (total mortality). The amount of vitamin E taken in the studies ranged from 50 to 800 IU per day, while the amount of beta-carotene was between 15 and 50 mg per day.
After pooling the results from the seven studies on vitamin E, no reduction in heart disease, stroke, or total mortality was found among participants who took supplemental vitamin E. Supplemental beta-carotene was associated with a slight, but statistically significant, increase in cardiovascular death and total mortality. The authors concluded that physicians should discourage people from taking supplemental vitamin E and beta-carotene and that both of these nutrients may be harmful.
Although the negative results are consistent with the findings from a few studies, other studies have shown a clear benefit from taking supplemental vitamin E. One study showed a 77% reduction in heart attacks after 18 months of supplementation with 400 or 800 IU of vitamin E per day. Other studies have shown that vitamin E significantly improves walking distance and reduces pain in those with hardening of the arteries (atherosclerosis) in the legs. Evidence for supplemental beta-carotene in preventing heart disease is lacking. Some critics point out that most of the studies have used synthetic beta-carotene, which may have different biological activity than natural beta-carotene. However, more research is necessary to clarify that issue.
The conflicting results observed in various antioxidant studies may reflect differences in nutritional status among the individuals being studied. Vitamin E and beta-carotene are only two of many nutrients that play a role in maintaining good heart health; other important nutrients include magnesium, vitamin B6, folic acid, selenium, copper, zinc, and chromium. Studies that look only at single nutrients may be misleading if a combination of nutrients is required for the cardiovascular system.
In addition, meta-analyses may themselves be misleading if they combine the results of studies that differ in their design or in the populations studied. For example, at least seven small controlled trials have shown that giving intravenous magnesium during the early stages of a heart attack can reduce the death rate substantially. One very large study, however, which included more participants than all of the other studies combined, found no benefit of magnesium. Combining the results of all the studies led to the conclusion that magnesium is useless. The large negative study, however, used what appears to have been an excessive, and potentially toxic, dose of intravenous magnesium, whereas all of the positive studies used a smaller dose. Therefore, it was not appropriate to combine all of these studies into a single, larger study. The same may be true for studies that assessed vitamin E and beta-carotene, since different patient populations and a range of nutrient doses were studied.
Despite the impression left by the new study that vitamin E and beta-carotene are dangerous, there is some evidence that these nutrients are beneficial when included as part of a regimen that is tailored to the specific metabolic or nutritional needs of a person. With respect to beta-carotene, most research suggests that it is best obtained from food (such as various fruits and vegetables), rather than in supplement form. Beyond heart disease, antioxidants may also help prevent cancer and other degenerative diseases, such as Alzheimer’s disease. Perhaps future studies will more closely examine individual biochemical needs, which may provide more insight into who might benefit most from antioxidant supplementation.
Darin Ingels, ND, MT (ASCP), received his bachelor’s degree from Purdue University and his Doctorate of Naturopathic Medicine from Bastyr University in Kenmore, WA. Dr. Ingels is the author of The Natural Pharmacist: Lowering Cholesterol (Prima, 1999) and Natural Treatments for High Cholesterol (Prima, 2000). He currently is in private practice at New England Family Health Associates located in Southport, CT, where he specializes in environmental medicine and allergies. Dr. Ingels is a regular contributor to Healthnotes and Healthnotes Newswire.
Alan R. Gaby, MD, an expert in nutritional therapies, testified to the White House Commission on CAM upon request in December 2001. Dr. Gaby served as a member of the Ad-Hoc Advisory Panel of the National Institutes of Health Office of Alternative Medicine. He is the author of Preventing and Reversing Osteoporosis (Prima, 1994), and co-author of The Natural Pharmacy, 2nd Edition (Healthnotes, Prima, 1999), the A–Z Guide to Drug-Herb-Vitamin Interactions (Healthnotes, Prima, 1999), Clinical Essentials Volume 1 and 2 (Healthnotes, 2000), and The Patient’s Book of Natural Healing (Prima, 1999). A former professor at Bastyr University of Natural Health Sciences, in Kenmore, WA, where he served as the Endowed Professor of Nutrition, Dr. Gaby is the Chief Medical Editor for Healthnotes, Inc.