The molecules that make up the category vitamin A are all part of a group of compounds that exhibit the biological activity of retinol. Most dietary vitamin A is obtained from carotenoids or from animal tissues with high vitamin A content. Being a lipid-soluble vitamin, this nutrient in either large or chronic amounts can concentrate in fatty tissues and cause numerous symptoms of toxicity including headaches, bone pain, weakness, and skin problems, among others.
Vitamin A is known to be essential in vision, testicular function, development, bone growth, differentiation, and hematopoiesis. It has also been shown to possess antioxidant properties, offering protection against lipid peroxidation, oxidative modification of proteins, and LDL oxidation. Little research has been done examining the effects of vitamin A supplementation in athletes. This is potentially due to a few factors including the fact that vitamin A toxicity is likely at higher doses. In addition, although plasma vitamin A is decreased as a result of exercise in rats, skeletal muscle vitamin A is increased, indicating a homeostatic mechanism for antioxidant balance.
The term vitamin E refers to eight similar compounds- alpha, beta, delta, and gamma tocopherol and four tocotrienols of the same designations. The prefixes alpha through gamma refer to the number and position of methyl groups on the aromatic ring on the molecule. The difference is that the tocotrienols have three double bonds along the side chain of the molecule, whereas the tocopherols do not (tri means three, of course, and -ene refers to a carboncarbon double bond.) Members of the vitamin E family have direct biological relationships with immunity, aging, exercise, heart disease, and cancer.
Although alpha-tocopherol is the most abundant of these compounds in tissues and is the most bioactive and bioavailable, recent marketing attention has been placed on the use of mixed tocopherols and tocotrienol forms. This is due to the research that suggests that different vitamin E derivatives possess increased in vitro antioxidant activity as well as unique antioxidant and therapeutic properties The debate, however, continues as many question whether increased in vitro antioxidant capacity is beneficial when there is decreased bio availability of the compounds. This argument is supported by data showing that the old school alpha-tocopherol that has been popular for many years has superior biological potency.
Another concern regarding the intake of vitamin E is that because it is present primarily in fats, limiting dietary fat, as many athletes and health-conscious individuals do, will limit its availability. The health and antioxidant benefits of vitamin E have been well documented through numerous trials and have shown that the membranebound vitamin E is one of the cell’s predominant defense mechanisms against lipid peroxidation.
Vitamin E is continuously recycled by numerous other antioxidants including vitamin C, ubiquinone, and glutathione. In terms of exercise performance, Vitamin E is probably the most researched of the antioxidants. As with other antioxidants, improvement in performance trials has not usually been found with the exception of aerobic training at altitude and aerobic training in ozone-rich environments. In the studies that did show improvements, vitamin E improved both oxidation status and lactate threshold in mountain climbers; whereas in cyclists, vitamin E supplementation improved pulmonary function and oxidation status in the presence of ozone-rich air. Since ozone (found in polluted air) is a powerful oxidant that reduces lung performance, urban exercisers may benefit from vitamin E’s antioxidant characteristics. The benefits would primarily manifest as reduced toxicity rather than actual performance enhancement, however, as pulmonary oxygen provision is not generally considered limiting in aerobic performance.
Although performance may not be greatly impacted by antioxidant supplementation, perhaps the greatest potential benefit that vitamin E can offer athletes is a reduction in exercise-induced tissue damage. Although there are mixed results, the evidence is relatively convincing that vitamin E supplementation can decrease muscle and oxidative damage in response to exercise. First, it has been reported that consuming 800 IU/day of vitamin E can, in fact, elevate serum concentrations of alpha- and gammatocopherol by 300% and 74%, respectively. Thus, supplemental regimes with this vitamin are effectively absorbed. Second, these elevations subsequently induce substantial skeletal muscle increases of 53% and 37%, respectively, within 30 days. The results of these increases are encouraging for hard-training athletes. In various studies in humans and in animals, vitamin E supplementation has been shown to decrease plasma levels of the cytosolic enzymes creatine kinase and lactate dehydrogenase. In addition, markers of lipid peroxidation such as MDA, conjugated dienes, and TBARS have been reduced with vitamin E supplementation . Also, reperfusion injury in the quadriceps can be reduced with 600 IU/day of oral vitamin E over 8 days. The effect of vitamin E on protein catabolism needs further work, but in particular studies, vitamin E seems to possess beneficial effects.
Vitamin C is known as ascorbic acid and because of its solubility in aqueous environments, is most associated with both intracellular and extracellular fluids (blood). Although there is controversy regarding the proposed correlations between vitamin C and disease such as cancer, heart disease, or stroke, vitamin C is known to be an effective antioxidant. Vitamin C has the unique ability to act as a primary antioxidant by donating electrons to quench free radicals and reactive oxygen species and as a secondary antioxidant to regenerate vitamin E within the intracellular fluid. In addition to its interaction with vitamin E, oxidized vitamin C is reduced and recycled by glutathione. Due to its nonspecific antioxidant properties, vitamin C is effective in the removal of most reactive oxygen species. In exercise training, vitamin C has been shown to reduce free radical production during and after exercise. Also, vitamin C can reduce muscle soreness and improve recovery from muscle damage. In a study examining the eccentric muscle damage, maximum voluntary contractions were greater 24 hours after the damaging exercise when subjects supplemented with vitamin C than when they supplemented with vitamin E or placebo.