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Can you nourish your way to an illness-free winter?
Written by: Matt Fitzgerald
With the cold and flu season upon us, it’s important to ensure that our immune systems are up to the challenge. This especially holds true for runners, since high-volume training presents additional immune-system stresses. So does that mean you should be madly popping highly touted immune-boosting supplements such as zinc in an effort to fortify your defenses? Probably not. While I won’t go so far as to say that all such supplements are useless, the best available research indicates that the majority of them offer little to most athletes. Consider:
Glutamine. The amino acid glutamine, a vital source of energy for immune function, is one of the nutrients that runners commonly take for immune support and muscle recovery. The body uses glutamine at a very high rate during exercise. It is sent from the muscles to the liver and converted to glucose, which is then sent back to the muscles to provide energy. Plasma glutamine levels drop dramatically during prolonged exercise and remain low for some time afterward. This drop was once believed to leave the body more susceptible to bacterial and viral infections, and some early studies appeared to show that taking supplemental glutamine after exercise lessened exercise-induced immunosuppression and reduced the risk of infection. But more recent research has not supported these earlier findings, and in a 2008 review of the scientific literature in this area, Michael Gleeson of England’s Loughborough University reported that “glutamine supplementation does not prevent the post-exercise changes in several aspects of immune function.”
Zinc. The mineral zinc is contained in sweat, so there is some cause to speculate that endurance athletes might need to take supplemental zinc to maintain normal zinc levels and immune function. However, studies have shown that zinc levels are typically normal in non-vegetarian athletes even without supplementation, and that zinc supplementation does not reduce the incidence of upper respiratory tract infection in individuals with normal zinc levels. That said, because red meat is by far the best food source of zinc, athletes who eat little or no red meat should take a good daily multinutrient that contains zinc.
Magnesium. Magnesium is another mineral that is vital to immune function and lost in sweat. Based on these facts, Portuguese researchers recently raised the possibility that magnesium depletion could account for a portion of the immunosuppressive effects of strenuous exercise. If this is true, then it might be considered a good idea to use a magnesium-containing sports drink during exercise to limit magnesium depletion. But I believe that nutrient depletion of any sort is not the primary cause of the immunosuppressive effects of strenuous training, and that a long, hard workout is going to suppress your immune system for a short time no matter what sort of banquet you try to wolf down during it. That said, consuming a magnesium-containing sports drink is a beneficial way to maintain fluid balance during workouts, and it certainly won’t do your immune system any harm.
Carbohydrates. Perhaps the most popular nutritional method thought to boost the immune system during endurance exercise is carbohydrate consumption. In a number of studies, David Nieman, of Appalachian State University, has shown that consuming carbohydrate during prolonged exercise attenuates its normal effects on immune parameters. But these studies may be a classic example of how science sometimes produces misleading conclusions. The problem is that in Nieman’s studies, subjects were required to fast before their test workouts, so that they started exercising in an artificially carbohydrate-depleted state. But in a recent study from researchers at the Australian Institute of Sport in which subjects were allowed to eat a normal breakfast before their test workout, the beneficial effect of carbohydrate consumption during exercise disappeared because the immune function consequences of prolonged exercise were themselves reduced.
The one conclusion of Nieman’s research that this new study does not contradict, however, is that carbohydrate deficiency exacerbates the effects of hard training on immune function. Since most runners do not consume enough carbohydrate to optimize their training and racing, you can expect that, by increasing your carbohydrate intake for the sake of performance, you will also reduce the immune system strain imposed by your training. In other words, adding more carbs to a generally healthy diet should boost immunity as well as athletic performance.
Check out Matt’s latest book, RUN: The Mind-Body Method of Running by Feel.