Our faith in the power of antioxidants may be misplaced, according to new studies.Sales of orange juice are soaring as people seek flu protection from vitamin C, The Globe and Mail reported last month.
Old habits die hard, and our faith in the power of antioxidants is deeply entrenched. Over the past few years, a vast series of studies involving hundreds of thousands of subjects have failed to find any health benefits from antioxidant supplements.
Now, a handful of studies suggest that popping these pills may even block some of the benefits of exercise, and even slow down post-workout muscle recovery.
It would be premature to pronounce the end of the vitamin era on the basis of a few studies – as premature as it was to leap on the bandwagon in the first place – but some skepticism is due.
“For something like vitamin C, it's important to have enough,” says Stephen Cheung, a physiologist at Brock University. “But that doesn't mean more is better.”
Antioxidants – vitamins C and E as well as molecules ranging from beta-carotene to the currently fashionable resveratrol – attack and neutralize the “free radicals” associated with aging and disease. Exercise stimulates the production of free radicals, which is why athletes are often advised to take antioxidant supplements.
But exercise is itself an antioxidant, since the body gradually learns to produce more and more of its own antioxidants in response to the spike of free radicals generated by exercise. One theory now gaining support is that taking extra antioxidants means the body never gets the opportunity to adapt on its own.
In May, Michael Ristow and colleagues at the University of Jena in Germany published a study in the Proceedings of the National Academy of Sciences examining how a four-week exercise program affected insulin sensitivity – one of the most significant health benefits conferred by physical activity. Half of the 40 volunteers were given a placebo, and saw significant improvements in insulin sensitivity; the other half took 1,000 milligrams of vitamin C and 400 IU of vitamin E each day, and saw no change despite the exercise regime.
To Dr. Ristow, this suggests that antioxidants are unequivocally bad, even though the research in favour of eating fruits and vegetables is unimpeachable.
It implies that fruits and vegetables are healthy despite their antioxidant content, not because of it, and that “other compounds in fruit and vegetables are responsible for their health-promoting effects,” he explained in an e-mail exchange.
The idea that antioxidants can stave off some muscle damage and soreness caused by free radicals after heavy exercise has also taken a hit.
In a study published in the September issue of Medicine & Science in Sports & Exercise, Portuguese researchers studying the national kayak team found hints that a cocktail of antioxidants actually delayed muscle recovery after training when compared with a placebo.
Victor Hugo Teixeira of the University of Porto, the study's lead author, speculates that free radicals may serve as a natural brake to prevent excessive exertion, while antioxidants override that signal and allow the muscles to work a little harder and sustain greater damage.
If that's true, athletes might benefit from taking antioxidants right before a competition, but would impede their recovery from training by taking them on a regular basis.
Even if antioxidants do ruin your workout, many people would gladly take that risk if it helped them avoid the flu. It is well established that they can help boost immune function in people who have undergone extreme physical exertion, such as ultramarathoners, Dr. Cheung says. But it's less clear that the same benefits accrue in everyday life.
In a study published last year, Dr. Cheung had volunteers cycle at moderate intensity for two hours – hardly slacking – and tested whether their immune function was helped by 1,500 milligrams of vitamin C a day for two weeks afterward.
The results were equivocal: If there was any effect, it was weak.
Dr. Cheung's advice is to ensure you are getting enough vitamin C from your diet, and if not, to change your diet before resorting to supplementation.
In a field where the science is still hotly contested, this seems like wise counsel. Some day, perhaps, we'll know exactly which molecules make fruit and vegetables so good for us – but until then, as long as you're eating lots of them, you don't have to worry about which ones.
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