Historical and scientific evidence demonstrate that vitamin C deficiency or even marginal vitamin C status can adversely affect physical performance. Ascorbic acid can adversely affect physical functioning at several different metabolic sites such as: impaired collagen formation leading to increased ligament and tendon problems; decreased synthesis of carnitine ,which would impair the use of fatty acids as an energy source; decreased synthesis of epinephrine and norepinephrine resulting in improper metabolic responses to exercise; as well as improper iron metabolism possibly resulting in anemia and fatigue with consequential decreases in aerobic performance. Thus, all physically active persons should strive to maintain optimal vitamin C status through intake of generous servings of fruits and vegetables high in ascorbic acid, or if this is not possible, through proper supplementation with the vitamin through pills or with foods that have had vitamin C added. The RDA for vitamin C is 75 mg for adult women and 90 mg for adult men. These values may not be sufficient for athletes engaged in strenuous, prolonged physical activity events and training. Appropriate intakes for these athletes may range from 100 to 1000 mg each day.
Numerous studies have investigated both the effects that exercise has on vitamin C needs and the effect that supplemental vitamin C has on subsequent athletic performance. Several animal and human studies do seem to indicate that strenuous or prolonged exercise or physical training, in all likelihood, increases the need for vitamin C. It is less likely that light or moderate levels of activity and training increase vitamin C requirements. Animal studies consistently show reduced tissue levels of ascorbic acid with exercise. Several human studies have shown reduced plasma and leukocyte concentrations and reduced urinary excretion of the vitamin with exercise. In addition, supplemental dietary vitamin C has been shown to increase adaptation to exercise in the heat and reduce upper respiratory tract infections in individuals undergoing strenuous exercise. Supplemental vitamin C also has been shown, in some studies, to reduce plasma cortisol concentrations and muscle soreness markers following exercise. Vitamin C intake in these studies generally ranged from 100 to 1500 mg/day. Numerous other data from dietary intake studies with athletes show mean vitamin C intakes of most athletic groups to be in the 55 to 850 mg/day range; intakes that are generally above RDA values. However, several of these studies report that up to 25% (or perhaps more) of the athletes consumed vitamin C at less than RDA levels. Thus, while mean ascorbic acid intakes appear to be adequate, a large percentage of athletes could be consuming suboptimal intakes of the vitamin.
Numerous studies have been conducted in an attempt to find possible ergogenic effects of ascorbic acid. The results of these studies are mixed. Many report possible ergogenic effects of vitamin C, while just as many studies find no effect of ascorbic acid supplementation on subsequent performance. Most of the more recent, and generally better controlled studies do not seem to indicate an ergogenic effect of vitamin C. At the present time, the data do not seem to support a clear or consistent ergogenic effect of vitamin C.
While a wealth of knowledge does exist concerning ascorbic acid and exercise, many areas remain understudied. The relationship between exercise and vitamin C requirements is still one such area. Most of the work done in this area has been performed with runners. Little or no work has been done that has reported on the relationships between vitamin C requirements and exercise for strength-power athletes, swimmers (who undergo large training volumes) and cyclists. Studies on plasma and leukocyte ascorbic acid concentrations and changes, as well as urine excretion values, cortisol concentration changes and upper respiratory tract infections in these groups have not been performed. Little, if any, work has been performed evaluating how exercise might alter ratios of ascorbic acid and dehydroascor-bic acid in tissues. This ratio has been shown to be altered in some disease states. Newer studies looking at the effects of ascorbic acid on heat acclimation need to be done. Heat stress and dehydration are extremely important concerns for many athletes. No studies have investigated the relationship between heat stress and vitamin C for more than 25 years. All of these subjects need to be explored in the future to further our understanding of vitamin C and physical activity.
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