Vitamins are organic compounds that help the body perform highly specific metabolic functions, but do not directly supply energy or serve as structural components of body cells. As such, they are catalysts in the metabolic pathways that convert fats, carbohydrates, and proteins into Calories or energy - facilitating the reactions, but not being "used up" or consumed by them. This explains why recommended daily requirements are independent of body size or daily energy expenditures.
Does a physical training program result in vitamin or mineral deficiencies? It is generally agreed that the vitamin needs of physically active people are no greater than those of sedentary individuals. However occasional papers have suggested that an imbalance might occur among athletes, and trainers and athletes, hoping to avoid any possible deficiency that would impair performance, have leapt onto the vitamin and mineral supplement bandwagon. And the placebo effect is so strong that some athletes have actually been reported to become psychologically dependent on high dose supplements.
Vitamins are classified as water soluble or fat soluble. The fat soluble vitamins (A,D,E, and K) are primarily stored in the liver and fatty tissues, and can be accumulated to levels that may be toxic. Water soluble vitamins (B and C) are not stored in the body to any appreciable extent, are eliminated in the urine, and must be resupplied on a regular basis by the diet. There is evidence that mega-vitamin programs can be harmful, particularly with the fat soluble vitamins which are not eliminated in the urine. And there have been occasional reports that even the water soluble vitamins (B complex, and C which are excreted in the urine if excess amounts are taken) can be harmful at doses of 10 to 100 times the recommended daily requirements (RDA).
RDAs have been determined by numerous governmental and professional organizations, and as a result may not be identical. They are usually expressed as ranges, and generally speaking supplementation is recommended only when dietary intake drops below 2/3 of the RDA for that specific nutrient. Most dietary surveys of athletic populations have indicated that these groups easily exceed the RDA when a well balanced, isocaloric diet replacing daily expenditures is consumed. The exceptions are athletes on weight loss diets or who participate in sports that glorify unrealistically low body fat levels. In other words, a low Caloric intake increases the chance that vitamin intake will be below the RDA.
VITAMIN SUPPLEMENTS AND EXERCISE PERFORMANCE
There is little question that vitamins will improve performance in athletes with preexisting vitamin deficiencies. And it has been speculated that the improvement of performance noted in several papers was the result of treating unidentified, preexisting vitamin deficiencies. Several recent studies have been structured to avoid the weaknesses of these past papers, looking at the effect of vitamin supplementation of male and female athletes who were already consuming their RDA of vitamins through diet alone. One study covered a 6 to 7 month training period. While an increase in blood and tissue levels of multiple vitamins was demonstrated, there was no evidence of an effect on athletic performance. A second studied 22 men over a 90 day period, measuring maximal oxygen uptake, endurance capacity, and isokinetic strength. This double blinded, placebo controlled study failed to demonstrate any performance advantage of vitamin supplements. Thus the perceived need for vitamin supplements is based on anecdotal reports not on firm scientific evidence. And the use of high potency multivitamin formulations are potentially toxic as well as supporting poor nutrition as athletes feel the supplement eliminates the need to eat a balanced diet.
As opposed to their effect on performance, there is some intriguing data on the positive health effects of antioxidant vitamins to minimize free radical damage to the cells. Exercising muscles generate oxygen centered free radicals which can harm cell organelles such as the mitochondria. Vitamin E, beta Carotene, and vitamin C are all nutritional antioxidants with Vitamin E appearing to be the most effective against these exercise induced free radicals. Two studies, one using 330 mg of Vit E for 5 months during extreme endurance training in cyclists, and another using 800 IU daily for 48 days demonstrated a significant reduction in serum creatine kinase (a muscle enzyme) and microscopic cellular injury (but no change in physical performance).
MINERAL SUPPLEMENTS AND EXERCISE PERFORMANCE
Minerals are chemical elements essential for normal cell functioning Calcium and phosphorus are major components of the bodyís bony structures while sodium and potassium are found in all tissue fluids both within and around cells. The trace elements magnesium, chloride, sulfur, and zinc play a key role in cell function while iron, manganese, cobalt, selenium copper, and iodine are found in much smaller quantities and play essential roles as catalysts in cellular chemical processes.
These minerals, found in all foods, are kept in balance through internal regulation of absorption and excretion. As a result, adequate tissue levels are easily provided by a balanced diet. As with vitamins, multiple studies of body tissue mineral status in athletes failed to identify any deficiencies in those ON A BALANCED DIET compared to people engaged in normal daily activities. Athletes who are restricting energy intake to achieve a lower body weight (endurance runners for example) are the exception, and may need supplements.
Sodium is the only mineral that, as a supplement, may improve endurance performance by preventing hyponatremia (a low blood sodium concentration), although recent evidence suggests that it is the excess consumption of pure water that is the culprit, not the lack of sodium. Aside from sodium, there is no evidence that the use of any single or combination of electrolyte supplements enhances physical performance. And except for iron deficiency (with documented low hemoglobin levels) the same holds true for the trace minerals supplements.
As with vitamins, there have been several well controlled, blinded studies on the effect of trace mineral supplements on performance. These have looked at such parameters as muscle glycogen depletion, serum free fatty acids, maximal aerobic capacity, and endurance abilities. Absolutely no benefits were identified in the group using the supplements. And side effects were even more common than with vitamins including such non specific complaints as nausea, malaise, and easy fatiguability.
The bottom line is that an athleteís vitamin and nutritional needs are readily and easily met by a balanced, isocaloric diet replacing daily Caloric expenditures. If there are special dietary considerations ( a negative Caloric balance for example), or a concern about how well balanced the diet may be, there is no harm (other than to the wallet) in using a simple over the counter multiple vitamin once a day. But vitamin and mineral supplements are not the easy answer to increased performance.