Nutritional supplements and athletic performance

Performance-enhancing dietary supplements are regularly used by competitive athletes and daily exercisers. Surveys indicate that 75% of college athletes and almost 100% of body builders use at least one product that allegedly boosts performance.

These supplements are often called "ergogenic aids"—the general term for ingested substances that improve efficient use of energy, increase energy production, or shorten recovery time. The ergogenic aid industry has shown steady upward growth, with new products entering the market weekly. But there is little evidence that the billions of dollars spent on performance enhancers provide the advertised results.

Unlike medications that need to be approved by the U.S. Food and Drug Administration (FDA), dietary supplements can be sold without such preapproval. The FDA has used its limited authority to enhance the safety of supplements and to pressure manufacturers to accurately label ingredients. The FDA has been more aggressive about stopping promotions and advertisements claiming false benefits. But the agency has a daunting task, because there are so many products, and it has to prove that the products are unsafe or that the promotions are untruthful.

High dose vitamins and minerals

Although special preparations of high-dose vitamin and mineral supplements are widely advertised as performance enhancing, there is no evidence that mega doses do more than a well-balanced diet. According to the American College of Sports Nutrition, an athlete who is regularly consuming a diet that provides sufficient protein and calories, and contains plenty of fruits and vegetables, should not need extra vitamins and minerals.

There are two situations where exercisers might benefit from certain supplements: one is if you are a strict vegetarian, and another if you are a menstruating woman. During exercise, more than the usual amounts of B vitamins are needed. These include thiamin, niacin, riboflavin, pyridoxine, and pantothenic acid. Enriched cereals and whole-grain carbohydrates combined with some lean meats will satisfy the needs of even the extreme athlete

Vegetarians and other competitors on restricted diets may not get enough vitamins and minerals from food. They many need to take some supplements, such as vitamin B12 and iron.

Women often need extra iron to replace monthly blood loss from menstruation. A daily generic multiple vitamin with iron is inexpensive and safe insurance if there is any concern that your diet is not providing all that you need.

In general, antioxidants do not enhance performance. The one exception may be vitamin E for high-altitude exercise. One study showed that athletes taking vitamin E at a dose of 400 international units per day had more stamina at high elevations compared to those taking a placebo. Most other studies have not shown vitamin E to be superior to placebo at lower altitudes.

Some of the antioxidant vitamins, such as vitamins C and E and beta carotene, may lessen muscle soreness following exercise by neutralizing free radicals that contribute to exercise-induced muscle damage. The evidence is not conclusive, though and the proper doses have not been established. Supplemental doses up to 6 milligrams of beta carotene, up to 500 milligrams of vitamin C, and up to 200 units of vitamin E are reasonable for this purpose.

Amino acid and protein supplements

Most amino acids and proteins are not performance enhancing. You do need adequate protein intake to exercise at high-performance levels, but extra protein does not provide a boost. A person who gets little exercise needs only 0.36 grams of protein per pound of body weight daily. Someone exercising vigorously or body building would rarely need more than twice that amount, or about 100 grams of protein per day for a man who weighs 150 pounds.

Popular protein supplements often highlight the fact that they contain certain amino acids, such as creatine, carnitine, and the branched-chain amino acids (isoleucine, leucine, and valine). Creatine is the one amino acid that may have some athletic benefit. It contributes to rapid energy production and may enhance power or speed bursts that require short periods of anaerobic activity. It does not build muscle or increase endurance, and it can result in water retention. Long-term effects are unknown.

Carnitine, another amino acid, has been hyped based on the hope that ingesting more could increase energy, burn more fat, and produced weight loss. But the carnitine in supplements does not make its way into the body's cells and the kidney must do extra work to get rid of it.

The branched-chain amino acids are metabolized by muscle, and this has led to unsubstantiated theories of why they improve performance. In fact, they do not provide additional energy above and beyond other nutrients. Multiple studies have failed to show a benefit to exercisers who take them. 

Too much dietary protein and amino acids can have adverse consequences, such as dehydration, gout, kidney stones, and higher risk of osteoporosis.

What are your thoughts about vitamin, mineral, amino acid and protein supplements? Do you find them helpful? How do you decide what to try?

Howard LeWine, M.D., is a hospitalist at Brigham and Women's Hospital in Boston, where he practices and teaches Internal Medicine. He is the Chief Medical Editor of Internet Publishing at Harvard Health Publications.

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