Efficacy of nutritional supplements used by athletes.

Findings on the efficacy of nutritional supplements used by athletes are reviewed. Many athletes have turned away from anabolic steroids and toward nutritional supplements in the hope of gaining a competitive edge without threatening their health. Athletes may require slightly more protein than sedentary people do to maintain positive nitrogen balance, but it is dubious whether extra dietary protein will help someone to achieve athletic goals. Purified amino acids have become a popular if expensive form of protein supplementation; there is no scientific evidence, however, to support their use. Excessive protein supplementation can lead to dehydration, gout, liver and kidney damage, calcium loss, and gastrointestinal effects. Supplementation with vitamins and minerals in excess of recommended daily allowances appears to have no effect on muscle mass or athletic performance. Other substances touted as having ergogenic properties are carnitine, cobamamide, growth hormone releasers, octacosanol, and ginseng; again, there is no reliable scientific evidence to support claims that products containing these compounds have ergogenic potential, and heavy supplementation may lead to adverse effects. Nutritional supplements are promoted through unsubstantiated claims by magazine advertisements, health food stores, coaches, and other sources. The FDA considers nutritional supplements to be foodstuffs, not drugs, and therefore has not required that they be proved safe and effective. Dosage guidelines are inadequate, and quality control is poor. The FDA has begun to revise regulations governing labeling and health claims for these products. There is little if any evidence that nutritional supplements have ergogenic effects in athletes consuming a balanced diet, and some products have the potential for harm.