Exercise

February 9, 2012

Is Antioxidant Supplementation Useless?

A dozen or so years ago, I was given a book to read called “The Antioxidant Miracle.” The book, written by researcher Lester Packer, discussed the (apparent) plethora of benefits of taking antioxidant supplements–benefits that included a reduced incidence of heart disease and cancer, healthier skin, and even better sex! The skeptic that I am, I decided to look into the research and assess the validity of these claims.

First a little background info on the topic: In case you don’t know, antioxidants scavenge unstable molecules called “free radicals” that have been implicated in disease and aging. Here’s a short-course in how the process works: Your body is made up of billions of cells held together by a series of electronic bonds. These bonds are arranged in pairs so that one electron balances the other. However, in response to various occurrences (such as oxygen consumption), a molecule can lose one of its electron pairs making it an unstable free radical. The free radical then tries to replace its lost electron by stealing one from another molecule. This sets up a chain reaction where the second molecule becomes a free radical and attacks a third molecule, which becomes a free radical and attacks a fourth molecule and so on. The main culprit: oxygen. Every time you breathe, oxygen uptake causes free radical production. Environmental factors such as pollutants, smoke and certain chemicals also contribute to their formation.

To prevent rampant free radical production, your body has a sophisticated internal antioxidant system. Various antioxidant enzymes combine with antioxidants from the foods you eat to help keep free radicals at bay. But when free radical activity reaches a critical level, the system can become overwhelmed, causing extensive damage to cellular tissues.

Given my role as an exercise scientist (as well as the fact that I’m an avid exerciser), free radical buildup was of particular concern. After all, free radicals are generated by oxygen consumption and when does oxygen consumption skyrocket? During exercise, of course!

So I began poring over the peer-reviewed literature in an attempt to evaluate the potential benefits of supplementation. Lo and behold, the research seemed pretty compelling. There were numerous studies showing that taking antioxidant supplements had a positive effect on a multitude of health issues. Vitamin C, vitamin E, alpha-lipoic acid, co-Q 10 and other antioxidants all had shown efficacy with respect to improving health and preventing disease. Moreover, there seemed to be a synergistic effect of combining supplements. A red flag was that the studies were almost all observational and thus low on the hierarchy of evidence-based practice. Nevertheless, the studies included several large-scale trials and the sheer number of positive studies gave credence to positive benefits. I jumped on the antioxidant bandwagon…

As it turned out, this was an important career lesson for me. Subsequent studies (including a number of randomized clinical trials–the top of the evidence-based hierarchy) failed to find support for benefits of taking antioxidant supplements. In fact, some recent studies actually showed a *negative* effect of supplementation on markers of health and wellness. A 2008 systematic review published in the Cochran Database (Bjelakovic et al., 2008) refuted the claims that antioxidant supplements could prevent mortality in healthy people or patients with various diseases. The authors went on to conclude: “We found no evidence to support antioxidant supplements for primary or secondary prevention. Vitamin A, beta-carotene, and vitamin E may increase mortality. Future randomised 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.” A pretty sobering rebuke of earlier research.

For those who exercise, things become even murkier. Turns out that reactive oxygen species (ROS) actually function as key cellular signaling molecules in the response to exercise, and serve to bring about important training-related adaptations. They seem to be particularly important in adaptations to aerobic exercise, where oxygen is utilized at a very high rate. In accordance with this theory, a number of studies have shown that antioxidant supplementation can actually cause decrements in athletic performance. In a recent letter to the editor at the American Journal of Physiology Endocrinology and Metabolism, Gomez-Cabrera et al. cite some of the research on the subject and point out that antioxidant supplementation may be worse than useless for aerobic athletes–it has the potential to be detrimental.

Although the effects of antioxidants on resistance training have not been as well studied, there is good reason for concern. ROS have been shown to promote growth in both smooth muscle and cardiac muscle, and they are theorized to have similar hypertrophic effects on skeletal muscle. Interestingly, transgenic mice with suppressed levels of selenoproteins, a class of proteins that function as potent antioxidants, display increased exercise-induced hypertrophy, suggesting that the higher levels of ROS may play a role in muscle growth.

Now before we say case closed and demonize antioxidant supplementation as useless, realize that research on the subject is still in its infancy. There is still much we don’t know about the relationship between antioxidants, health, and exercise performance. Could it be that certain antioxidants are beneficial while others are not? Or could it be that a threshold of intake is beneficial while beyond this amount detrimental effects occur? We simply don’t know yet. So based on current evidence (which is all that we can go on at this point), it seems prudent to avoid taking supplemental antioxidants and instead focus on getting these nutrients from the foods you eat (vegetables and fruits are replete in antioxidants and other potentially beneficial phytochemicals). When future research comes out on the topic, we can then reevaluate recommendations.

Brad

Reference:
Bjelakovic G, Nikolova D, Gluud LL, Simonetti RG, Gluud C. Antioxidant supplements for prevention of mortality in healthy participants and patients with various diseases. Cochrane Database of Systematic Reviews 2008, Issue 2.