Antioxidant vitamins, exercise and muscle damage: another nail in the coffin?
Back in May, there was a flurry of excitement about a study suggesting that antioxidants might block some of the beneficial effects of exercise (heightened insulin sensitivity, to be specific). A new study in this month’s issue of Medicine & Science in Sports & Exercise now offers additional evidence for another proposed downside of antioxidant supplementation. According to a University of Porto study of 20 kayakers on the Portugese national team, popping anti-oxidant pills may delay muscle recovery.
Here are the details of the study. The kayakers were divided into two matched groups of 10. Each group did a hard 1,000-metre time trial, then received four weeks of either a placebo, or a pill containing “136 mg of alpha-tocopherol, 200 mg of vitamin C, 15 mg of beta-carotene, 1 mg of lutein, 200 Kg of selenium, 15 mg of zinc, and 300 mg of magnesium.” During these four weeks, the kayakers were in a national-team training camp, eating the same meals and doing the same training. At the end of the study period, they did another 1,000-meter time trial. Their blood was tested before and after the time trials.
Intense exercise produces free radicals (and other “reactive oxygen species”) that can cause oxidative damage to cells in the body, and it has long been thought that this could be one of the reasons that intense exercise produces muscle damage even after it’s over. These free radicals may also contibute to muscular fatigue during exercise — so it makes sense that taking antioxidants, which neutralize free radicals, could minimize post-exercise muscle damage and possibly even enhance performance during exercise. (It should be noted that exercise itself is an antioxidant, but it’s unable to keep up with the flood of free radicals produced by really intense exercise.)
The problem is that this doesn’t seem to happen in the real world — at least not with any consistency or predictability. In this case, the placebo group managed to lower its levels of creatine kinase (an indicator of muscle damage) more than the supplement group during the study period. This is far from being a smoking gun — the interpretation is still fairly complex. It may be that antioxidants DO work the way we think, allowing muscles to work a little harder in the heat of the moment, and that’s why we end up with more damage later:
We must considerer that [free radical]-mediated decline in contractile function can be a protective mechanism to limit further muscle injury and that the use of [antioxidant] supplements can override that protection, causing greater exercise-induced damage and increasing recovery times.
When you consider that hypothesis, the conclusion you draw is that acute supplementation right before a competition or intense workout might help you, but chronic (i.e. daily) supplementation will make you recover more slowly. But even that idea doesn’t have much actual, practical evidence to back it up. For the moment, the strongest conclusion I can come up with is the save your vitamin money and use it to buy some nice fresh berries.