Williams, M. H. (2004). Dietary supplements and sports performance: Introduction and vitamins. Journal of the International Society of Sports Nutrition, 1(2), 1-6.

This article reviews literature associated with vitamin and mineral supplementation in sports.

• Vitamin deficiencies impair sports performance in both aerobic and anaerobic factors.
• The effects of specific vitamins (e.g., B vitamins and choline) have been equivocal. Some contradictory effects of exceptionally high levels of B vitamins on fine motor performance have been reported. Choline, an amine involved in the formation of acetylcholine, is hypothesized as affecting fatigue but contradictory findings have been published.
• Multivitamin/mineral supplements are unnecessary for athletes on a well-balanced diet.
• Antioxidants (e.g., vitamin C and E) do not enhance performance. There are contradictory reviews about whether antioxidants prevent exercise-induced muscle damage. Although animal studies appear promising, effects in humans are less demonstrable. At most, it appears antioxidants might benefit some individuals but not others. How that responsiveness is determined has not yet been defined.
• Excess amounts of vitamins, that is, values in excess of the recommended daily amount, may exceed individual tolerability producing detrimental health effects. The contamination of multivitamin/mineral supplements with banned substances is a threat that is worth noting.

Implication. "In general, health professionals indicate that vitamin supplements are not necessary for the individual on a well-balanced diet, but they may be recommended for certain individuals, such as the elderly, vegans, and women of childbearing age. Moreover, some health professionals note that most people do not consume an optimal amount of vitamins by diet alone and indicate that it appears prudent for all adults to take vitamin supplements. In such cases, there is no need to take more than 100-150 percent of the RDA. Obtaining adequate vitamins, including use of supplements, may also be prudent behavior for some athletes. . . . athletes involved in heavy training may need more of several vitamins, such as thiamin, riboflavin and B6 because they are involved in energy production, but the amount needed is only about twice the RDA and that may be easily obtained through increased food intake associated with heavy training. . . . several sport nutrition experts indicated that some athletes may be at risk for a vitamin deficiency, such as those in weight-control sports and those who for one reason or another do not eat a well-balanced diet. . . . the prudent use of antioxidant supplementation can provide insurance against a suboptimal diet and/or the elevated demands of intense physical activity, and thus may be recommended to limit the effects of oxidative stress in individuals performing regular, heavy exercise".

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