In addition to glutamine, there has been interest in determining the role that other nutrients may have on immune function. From these studies, there appear to be several nutrients and or herbs that may help athletes maintain a healthier immune system during training. The first nutrient reported to enhance immune function is protein Studies indicate that immunosuppressed patients are often protein malnourished. Additionally, athletes who maintain a negative energy balance during training may also be susceptible to become protein malnourished. Protein supplementation in protein-malnourished patients has been shown to improve immune status Consequently, it is important that athletes eat enough quality protein in their diet to maintain a healthy immune system.

The second nutrient that may affect immune responses during training is vitamin C. Vitamin C is involved in the synthesis of epinephrine, iron absorption, and is an antioxidant. There is also evidence that vitamin C may enhance immune function. With regards to athletes, vitamin C supplementation (600 mg/day for 3 weeks) following an ultramarathon race was found to decrease the incidence of URTI by 33% following the event in comparison to athletes given a placebo These findings have led some to contend that athletes engaged in intensified periods of training should supplement their diet with vitamin C to help decrease the incidence of URTI.

More recently, zinc supplementation (25 to 100 mg/day) during the onset of symptoms of a cold or URTI has been reported to decrease the severity and length of the cold infection. Athletes have been reported to be commonly zinc deficient. Theoretically, zinc supplementation during intensified periods of training and or as athletes experience symptoms of a cold may help athletes stay healthier. To support this theory, one study reported that zinc supplementation (25 mg/day) during training minimized exercise-induced changes in immune function. However, more research is needed to test this hypothesis.

The last supplement that may be beneficial for athletes to enhance immune function is echinacea. Echinacea is a popular herb that has been reported to enhance the immune system in a similar manner as an antibiotic. Evidence suggests that echinacea can reduce the incidence, severity, and duration of colds and infections Theoretically, echinacea supplementation during periods of intensified training and/or as an athlete experiences symptoms of a URTI may help athletes stay healthy during training. However, although there is scientific support for use of echinacea, we are not aware of a study that has evaluated whether echinacea supplementation during training affects the incidence of URTI in athletes.

As a result of training, all of the various oxidative processes are elevated in both aerobic and anaerobic athletes. The magnitude of these elevations depends on the intensity and type of exercise in which one is engaged. Also, some authors have speculated that the oxidative muscle damage associated with exercise may lead to the termination of muscular effort. In light of this knowledge, researchers and lay people alike have speculated that antioxidant supplementation may level the playing field, reducing tissue damage and soreness, improving exercise performance, and even prolonging life span. But do we need nutritional supplements to protect us from oxidative damage Or can our bodies handle the stress naturally through homeostasis?

Regarding antioxidant homeostasis, most of the research done on endogenous antioxidant enzymes and their adaptation to exercise has been done using endurance protocols. From this research, aerobically trained individuals (including humans and rats) have elevated endogenous (produced within) antioxidant enzyme concentrations and/or activities compared with controls As the body adapts to the demands of an increased training load by increasing mitochondrial density, capillarization, stroke volume of the heart, etc., it also defends itself from the increasing amount of oxygen that is delivered and used by the muscle. Because mitochondrial density increases (there are more mitochondria per unit of muscle) in aerobically trained individuals and the antioxidant enzymes are located within the mitochondria, it only stands to reason that antioxidant activity would increase in endurance-trained individuals. Of course, the more mitochondria, the more potential for reactive oxygen species, so the question is whether the increased enzymes can deal with the increased free radicals.

In numerous studies, the activities of the enzymes superoxide dismutase (SOD) and glutathione peroxidase (GPX) were increased in oxidative (type 1) skeletal muscle with endurance training. In addition, glutathione levels increase in response to training while oxidative damage is lessened when compared to untrained rats and humans. Although this suggests that trained individuals have a better protection from exercise-induced free radical damage than untrained, it cannot be assumed that the skeletal muscle of these individuals has enzyme levels that completely protect against free radical damage. Nor is it safe to assume that all athletes gain the same degree of antioxidant protection from training. Since enzymatic adaptations occur primarily in slow-twitch muscle fiber sand fast-twitch fibers do not, to a large extent, undergo such changes, athletes with a higher percentage of fast-twitch fibers like bodybuilders, sprinters, and power lifters may be more susceptible to free radical damage

The knowledge of training-induced endogenous antioxidant up regulation does, in fact, question the need for endogenous antioxidant supplementation. That is, why do athletes need an antioxidant boost when the body naturally adapts to exercise by improving its defenses Although the antioxidant capacity of the body is increased with endurance training, it appears that even these increases are often not sufficient to neutralize the increase in free radicals generated from long-duration aerobic exercise. It is clear that, depending on the type of exercise, free radical formation may supercede the body’s ability to protect itself, even in training-adapted individuals. In this case, it would be appropriate to increase the ingestion of exogenous antioxidants.

That said, the next relevant question would address whether the ingestion of foods that are high in bioavailable antioxidants would be sufficient to provide for the additional needs of specific populations or whether further antioxidant intake would be necessary. Since intense exercise training leads to the depletion of tissue and plasma concentrations of antioxidants such as coenzyme Q10 or ubiquinone, vitamin C, and vitamin E, this reduction may lead to a decreased antioxidant defense. This depletion is evident even in those athletes consuming a “nutritious, well-balanced, and mixed diet.” Hence, dietary intake may not provide sufficient amounts of antioxidants to athletes. By increasing tissue and plasma concentrations via antioxidant supplementation, athletes can assist endogenous antioxidant capacity and complement dietary intake to reduce the damage that results from strenuous training. Granted, antioxidants and nutrients seem to be better absorbed and seem to confer greater benefit when consumed as part of whole foods, but when whole food intake is insufficient, additional supplementation is the next best thing.