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LETTER TO THE EDITOR |
Boulder, CO
Brass and Hiatt [1] conclude after reviewing the literature that "available data do not support the use of carnitine administration to improve exercise performance in healthy persons." This is not the most reasonable conclusion to draw from the literature.
Available data, as the authors note, goes both ways. They are also correct in pointing out methodological flaws in many studies. Yet they underplay the positive results in many well-designed trials. Carnitine has been shown to allow athletes to exercise longer without fatigue [2]. Another study of 110 trained athletes corroborated this endurance enhancing effect [3]. A study of trained runners given 2 g of carnitine per day increased their peak running speed by 5.7% [4]. Carnitine supplements have been shown to help non-trained athletes achieve a "trained-like" state of greater endurance [5].
Carnitine is also useful for preventing muscle damage during vigorous exercise, especially in those who are not trained athletes [6]. This is due to is vasodilatation caused by carnitine which in turn leads to improved energetic metabolism of the muscle tissue. Carnitine also decreases lipid peroxide formation during exercise [7].
The most reasonable conclusion from the literature, which is clearly mixed, is that carnitine is a promising nutrient which may benefit athletes who perform aerobic sports. Carnitine research is still in its infancy. But there is at least reasonable scientific evidence to support the use of carnitine as an aid to aerobic performance.
REFERENCES
Harbor-UCLA Medical Center
Los Angeles, CA
University of Colorado
Colorado Prevention Center
Denver, CO
Author’s Reply
Carnitine "May" Benefit Athletes
In his letter, Mr. Crayhon identifies a challenge associated with evaluation of a number of dietary supplements. Specifically, the presence of a credible hypothesis and the publication of supportive data for a supplement is not equivalent to providing definitive proof of efficacy. Regulatory standards ensure that traditional pharmacologic products provide objective evidence for claims made. In the absence of such standards for dietary supplements, the scientific community must provide equivalent rigor in evaluating the available data.
Mr. Crayhon is correct in stating that there are published studies suggesting efficacy of carnitine to improve athletic performance. Gleim and Glace in their editorial [1], also emphasized that three of five studies cited were positive [2]. However, it is our opinion that critical review of these studies in the context of the overall literature does not allow a firm conclusion to be drawn. In a field such as this the issue of publication bias where small positive studies are more likely to be published then small negative trials also must be considered. Reports that do not distinguish between hypothesis, speculation and proven fact are potentially dangerous. For example, the evidence that carnitine is a vasodilator as suggested by Crayhon is very limited and in our opinion the compound is not vasoactive when given orally to man. Additionally, no automatic link between vasodilation and "improved energetic metabolism" can be inferred.
Mr. Crayhon concludes "... that carnitine is a promising nutrient which may benefit athletes ...". This is not incompatible with our statement that "... available data do not support the use of carnitine administration to improve exercise performance in healthy persons." It is our view that before a drug or nutrient can be recommended, data must definitively establish its efficacy. To date, this standard has not been met for carnitine. This does not mean it won’t be, and we strongly endorse the conduct of such clinical trials. In fact, if carnitine has a benefit of the magnitude suggested by Crayhon and others, these trials should not be hard to perform.
REFERENCES
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