Amino Acid Supplementation May Alter Hormone Levels Without Improving Performance

From the WebMD Archives

Jan. 7, 2000 (Tuscaloosa, Ala.) -- A large oral dose of a mixture of amino acids appears to have altered the hormonal balance of moderately conditioned athletes, according to a preliminary study published in the December issue of Medicine and Science in Sports and Exercise. However, experts who reviewed the article for WebMD point out that it is unknown whether the supplemental amino acids can improve athletic performance. They warn that the study is not strong enough to support recommendations for supplemental dosing of amino acids.

The study, by Luigi Di Luigi and colleagues at the Endocrine Research Laboratory of the Sports Medicine Unit of the University Institute of Motor Sciences in Rome and from the division of andrology at the University of Rome, evaluated the effect of a mixture of amino acids on various hormones in 10 athletes.

Ten male volunteers, aged 25-29, drank an orange-flavored mixture of several amino acids, sugar, and water. Blood tests were taken at various times before and after the mixture was consumed to measure various hormone levels in the athletes.

The researchers found that the amino acid mixture may have stimulated the athletes' pituitary glands, increasing secretions of certain stress-and sex-related hormones, including growth hormone. They believe the mixture of amino acids, or possibly a single amino acid, "could be responsible" for increases in cortisol and testosterone in the blood of the athletes. However, the researchers emphasize that "further studies are required to evaluate whether amino acid supplementations could also have a direct action at testicular and adrenal levels in addition to the action we found at the pituitary level."

"I am surprised this study got published," says Melvin H. Williams, PhD, who reviewed the article for WebMD. Williams, a professor emeritus of exercise physiology at Old Dominion University in Norfolk, Va., is currently revising the sixth edition of his classic McGraw Hill textbook, Nutrition for Health, Fitness, and Sport. He says he will "probably not" be mentioning this study in his book.

"This is only a small-scale, preliminary study," he tells WebMD. "It did not include any data on performance. The only data that is potentially important from the standpoint of athletic performance would be the measurements of growth hormone."


And although the Italian researchers reported some increase in growth hormone at various times during the test, by the end of the experiment no significant increases in the absolute levels of growth hormone were found in the bloodstreams of the volunteers, Williams notes.

"Since the absolute level of growth hormone did not increase, this study has no clinical significance to practitioners or relevance to practicing athletics," he concludes. "It is very weak data. No one should use these results as a reason to go out and take amino acids."

New York University expert Gary Wadler, MD, who also reviewed the article for WebMD, agrees. The safety of ingesting large amounts of these substances has yet to be proven, according to Wadler, who is an associate professor of clinical medicine at New York University's School of Medicine. "Adverse effects have been associated with amino acids supplementation," he says. "The medical literature contains reports of dehydration, loss of urinary calcium, and blockage of the absorption of certain essential amino acids. Over the years there have also been isolated reports of kidney and liver damage and gout."

Regardless of reports of adverse effects from supplements, "What we have today is a climate of the supplement du jour," Wadler tells WebMD. "People have been looking for an athletic advantage using whatever means possible for the longest time."

Even though the Italian researchers warn that "the use of amino acid supplementation in humans has to be examined in terms of safety and effects on the endocrine system" and that "the use of such supplementation should occur only when necessary and with medical supervision," U.S. experts worry that the results of the study will be ballyhooed to support the sale of mixtures of amino acids.

"Madison Avenue marketers will take articles such as this one and use them to promote so-called performance-enhancing substances in very fanciful terms so they can make a bundle selling those substances to the public," Wadler says. "To jump to the conclusion that mixtures of amino acids will improve athletic performance is an unwarranted quantum leap."

Vital Information:

  • A new study found that supplementation with a mixture of amino acids stimulated the pituitary glands in athletes to secrete certain stress- and sex-related hormones, including growth hormone.
  • Though this study is only a preliminary examination of amino acid supplementation, the findings do not show that amino acid supplements can improve athletic performance.
  • The researchers recommend that this type of supplementation only be used under medical supervision, as it is associated with some negative side effects.
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