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Have You Had Your Antioxidants Today?

The Science of Medicine

Steven Novella

Volume 35.6, November/December 2011

A successful marketing campaign can be scarily effective—make a claim enough times and people will believe it. Then just take the claim for granted; it becomes something everyone knows and no one questions. Back it up with some “sciencey” razzle-dazzle and link it to a combination of fear and hope, and you can have an entire industry based on nothing but marketing hype.

Take antioxidants (or rather, don’t take them): if you believe the hype, then you want them in your food; you want to take them as pills; and you want the maximum most powerful antioxidants that can be found in nature (especially from some obscure tropical fruit). Unfortunately, the evidence does not support the claim that there are any health benefits to taking antioxidants.

The theory behind antioxidant claims sounds very compelling. Oxidants are chemicals (free radicals, also called reactive oxygen species or ROS) that are the products of metabolism; they are highly reactive and can cause damage to proteins and cells. This damage is a major contributor to aging and disease. Antioxidants neutralize these free radicals and prevent damage.

Unfortunately, medical science is rarely so clean and simple. This nice story is true, as far as it goes (the best lies always contain a kernel of truth). Twenty years ago this was the state of our knowledge of ROS and antioxidants, and there was legitimate hope that antioxidants would be a useful therapeutic tool. However, as research continued we learned that the picture is more complex: The body has evolved a natural defense against the onslaught of ROS. These compounds are called free radical scavengers or antioxidants (such as the protein superoxide dismutase and some vitamins like C and E) and their job is to gobble up ROS before they can damage cells.

In addition, some ROS actually serve a purpose in the body, for example as signals to cells or as neurotransmitters (nitric oxide). In fact, the body has evolved a balanced and complex system to maintain homeostasis between ROS and antioxidants. Influencing that system by taking large amounts of exogenous antioxidants may not be such a good idea. In other words, if a balance between ROS and antioxidants has evolved, there is no reason to believe that there are any benefits to tipping the scales in one direction—toward antioxidants. In fact, doing so may cause harm.

What does the actual clinical evidence show? Well, to find out we have to go claim by claim.

The best current evidence shows that antioxidant vitamins are of no use in improving cognitive function or in preventing dementia (Gray et al. 2008). If we look at other specific neurodegenerative diseases, the picture is a bit more complex. Some studies show that vitamin E (but not C) may slightly reduce the risk of motor neuron disease, but only in women (Wang et al. 2011). Overall, the evidence is ambiguous and does not support a benefit for treatment.

In Parkinson’s disease (PD) the picture is more complex. There is some evidence that eating foods rich in vitamin E may help prevent PD, but taking vitamin E supplements does not. So perhaps it is something other than the vitamin E in these foods that is of benefit, or perhaps eating healthy foods in general is simply a marker for some other variable that protects against PD. Other studies show a benefit from taking the vitamin supplements but not changing diet (Miyake et al. 2011). In other words, the evidence is ambiguous.

It is reasonable to conduct further research into antioxidants and degenerative diseases. Current evidence is mixed, without any clear benefit, but there is enough positive preliminary evidence to continue to study the potential of antioxidants in preventing degenerative diseases.

The evidence for taking antioxidant supplements in the general population is also less than definitive. In addition, it actually suggests the potential for harm. A comprehensive review published in 2008 concluded: “We found no evidence to support antioxidant supplements for primary or secondary prevention. Vitamin A, beta-carotene, and vitamin E may increase mortality” (Bjelakovic et al. 2008).

That’s right—there might be an increased risk of death from taking vitamins A and E. The data is far from definitive, but it shows that we cannot assume that supplements, even vitamins, are harmless. It also shows that we need to be humble with our simplistic theories of biology. Until the research has had time to fully explore a biological question, we should not be confident in our extrapolations to clinical effect. Therefore, even when the theory sounds good, we always need to do clinical studies to see what the net effects are in humans.

When it comes to antioxidants, there is still the potential that they may be useful in specific situations. At present, however, there is no evidence to support going out of your way to eat lots of antioxidants in food or to take antioxidant supplements. In fact, doing so may be harmful. This evidence is at odds with the overwhelming marketing hype that has successfully created an irrational demand for a dubious product.

References

Bjelakovic, G., D. Nikolova, L.L. Gluud, et al. 2008. Antioxidant supplements for prevention of mortality in healthy participants and patients with various diseases. Cochrane Database of Systematic Reviews 2008, Issue 2. Article No.: CD007176.

Gray, S.L., M.L. Anderson, P.K. Crane, et al. 2008. Antioxidant vitamin supplement use and risk of dementia or Alzheimer’s disease in older adults. Journal of the American Geriatrics Society 56(2) (February): 291–295, doi: 10.1111/j.1532-5415.2007.01531.x.

Miyake, Y., W. Fukushima, K. Tanaka, et al. 2011. Parkinson’s disease study group. Dietary intake of antioxidant vitamins and risk of Parkinson’s disease: A case-control study in Japan. European Journal of Neurology 18(1) (January): 106–13, doi: 10.1111/j.1468-1331.2010.03088.x.

Wang, H., É.J. O’Reilly, M.G. Weisskopf, et al. 2011.Vitamin E intake and risk of amyotrophic lateral sclerosis: A pooled analysis of data from 5 prospective cohort studies. American Journal of Epidemiology 173(6) (March): 595–602.

Steven Novella

Steven Novella, MD, is an assistant professor of neurology at Yale University School of Medicine. He is the host of the Skeptics’ Guide to the Universe podcast, author of the NeuroLogica blog, executive editor of the Science-Based Medicine blog, and president of The New England Skeptical Society.