Antioxidant vitamins and probiotics health benefits after exercise
Will taking antioxidant vitamins block the health benefits of exercise?
Every year when cold and flu season hits, sales of orange juice soar as people seek the protection of vitamin C. Faith in the power of antioxidants is deeply entrenched. But over the past few years, a series of vast studies involving hundreds of thousands of subjects has failed to find any health benefits from antioxidant supplements. Now, another group of studies suggests that popping these pills may even block some of the benefits of exercise and 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—just as premature as it was to leap on the vitamin 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 in St. Catharines, Ontario. “But that doesn’t mean more is better.”
Antioxidants—vitamins C and E plus molecules ranging from beta carotene to 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 extra antioxidant supplements. But exercise itself is also an antioxidant. During exercise, the body gradually learns to produce more and more of its own antioxidants in response to the spike of free radicals generated by working out. One theory now gaining support is that taking extra antioxidants means that the body never gets the opportunity to adapt on its own.
In 2009, Michael Ristow and his 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 mg of vitamin C and 400 IU of vitamin E each day and saw no change despite the exercise regime. To Ristow, this suggests that antioxidants are unequivocally bad, even though the research in favor of eating fruit and vegetables is unimpeachable. “This insinuates that fruit and vegetables are healthy despite their content in antioxidants,” he explains, “[so] other compounds in fruit and vegetables are responsible for their health-promoting effects.”
The idea that antioxidants can stave off some of the muscle damage and soreness caused by free radicals after heavy exercise has also taken a hit. In 2009, researchers studying the Portuguese national kayak team found hints that, compared with a placebo, a cocktail of antioxidants actually delayed muscle recovery after training. Victor Hugo Teixeira of the University of Porto, the study’s lead author, speculates that free radicals may serve as a natural brake to stop you from pushing too hard. Taking antioxidant pills could override that brake, allowing your muscles to work a little harder and sustain greater damage. If that’s true, athletes might gain an edge from taking antioxidants right before a competition but would suffer from impaired recovery if they took them on a regular basis.
Even if antioxidants did ruin your workout, many people would gladly take that risk if it helped them avoid the flu. It’s well established that antioxidants can help boost immune function in people who have undergone truly extreme physical exertion, like running an ultra-marathon, Cheung says. But it’s less clear that the same benefits accrue in everyday life. In a study published last year, Cheung had volunteers cycle at moderate intensity for two hours—hardly slacking—and tested whether their immune function was helped by 1,500 mg of vitamin C a day for two weeks afterwards. The results were equivocal: if there was any effect, it was weak.
Cheung’s advice is to ensure you’re 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. Someday, 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.
Should I be taking probiotics?
Over the last few years, grocery store shelves have been taken over by “helpful” bacteria. Particularly in the dairy section, foods now trumpet the presence of live cultures and the health benefits they offer. The general term probiotics refers to live micro-organisms that interact with the existing bacteria in your gut to produce a positive effect on your health. Some of the most common examples are bacteria that feed on lactose and are used in the fermentation process to produce yogurts and cheeses.
A number of studies have shown that certain probiotic strains can help boost immune function. For instance, antibiotics often kill off some of the beneficial bacteria that live in your gut, an outcome that can leave you susceptible to gastrointestinal problems like diarrhea. A recent analysis of 34 different studies concluded that several strains of probiotics (S. boulardii, L. rhamnosus, L. acidophilus, and L. bulgaricus) all reduced the risk and severity of antibiotic-related and traveler’s diarrhea. There’s also some evidence that probiotics can enhance the mucous lining of the respiratory tract, to help prevent viral infections like colds and coughs.
Because the extreme effort associated with something like marathon training can leave your immune system temporarily depleted, athletes have been particularly interested in the potential benefits of probiotics. In a 2008 study at the Australian Institute of Sport, 20 elite runners spent four months of winter training taking capsules containing either Lactobacillus fermentum or a placebo. By the end of the study, the number of days during which the runners reported symptoms of respiratory infection was 2.4 times higher in the placebo group than in the probiotic group, and the symptoms were more severe on average in the placebo group. The researchers also took blood samples that showed elevated levels of interferon gamma, a marker of immune function, in runners taking the probiotic.
Another study monitored 141 runners training for the Helsinki marathon, giving them capsules containing either Lactobacillus rhamnosus or a placebo for three months leading up to the race and monitoring them for a further two weeks afterwards. In this case, there was no difference in the number of respiratory infections or gastrointestinal “episodes” reported by the two groups.
However, there was a trend for GI problems to clear up more quickly in the probiotic group (2.9 days for problems before the marathon and 1.0 day after the marathon) compared with the placebo group (4.3 days before and 2.3 days after).
These results are definitely encouraging—the problem is that every individual strain of probiotic bacteria has different effects, and there’s not yet any consensus about which ones are best or how much we need to take.
Fortunately, this is one of those cases where it makes sense to incorporate foods like yogurt with live bacterial cultures into your diet even though the scientific research is still incomplete. Even if the probiotics don’t do anything for you, you’ll still have eaten a bunch of nutritious (and tasty) food.
Will vitamin D make me a better athlete?
In a 2009 study, researchers from the University of Manchester in Britain asked 99 adolescent schoolgirls to perform a series of one- and two-legged jumps, then took blood tests to see how much vitamin D they had in their bodies. There was a clear correlation: the more vitamin D, the higher, faster, and more powerful the jumps. To many, this was confirmation of what they’d suspected for some time: the “sunshine vitamin” could turn out to be the ultimate natural performance enhancer. But it’s not quite that simple.
D has been the star vitamin of the past few years, piling up study after favorable study even as the claims of its fellow vitamins are steadily being debunked. According to various studies, vitamin D fights cancer, builds bones, combats heart disease, tunes up your immune system, and provides a long list of other benefits.
Since it’s produced in the body as a response to ultraviolet light from the sun, people who live far from the equator are particularly at risk of deficiency in winter—which may explain why diseases like lung cancer and breast cancer are most likely to kill you if you’re diagnosed during those gloomy months. You can get some vitamin D from sources like fatty fish and fortified milk, but the vast majority comes from either sunlight or supplements.
Interest in the sun’s potential as a performance booster dates back at least to a rudimentary Russian study in 1938 in which four students improved their 100-meter dash time by 7.4 percent after a course of UV radiation, while controls improved by only 1.7 percent. In subsequent decades, German researchers also tried boosting performance using sun lamps and identified vitamin D as the probable cause.
But this research petered out in the 1960s without any rigorous conclusions. Other studies have looked at vitamin D’s links with parameters like reaction time and muscle protein synthesis. But, according to a 2009 review of the topic in Medicine & Science in Sports & Exercise, no studies have ever looked for direct links between athletic performance and levels of vitamin D indicated by blood tests.
Much of the debate centers on how you define deficiency. According to a 2008 study in the American Journal of Clinical Nutrition, vitamin D levels in American children and adults appear to have declined since the 1980s, possibly because people spend less time in the sun and drink less milk. About half of adults now have sub-optimal levels of vitamin D, according to the study.
Notably, three-quarters of the girls in the University of Manchester study were found to be vitamin D deficient, which makes it less surprising that higher levels improved jumping performance. After all, even a glass of water is performance-enhancing if you’re thirsty.
Several large-scale studies involving thousands of people are now in progress to untangle the cause-and-effect links between vitamin D and various diseases. Despite the uncertainty, there’s enough evidence to suggest that you should be aware of your vitamin D levels and make sure you either take supplements or get enough sun.
Once you reach “normal” levels, there’s currently no evidence that further vitamin D will make you a better athlete—but going from deficient to normal could definitely put a spring in your step.