Creatine: a review of efficacy and safety.

OBJECTIVE: To provide an overview of the data on the efficacy and safety of the nutritional supplement creatine. DATA SOURCES: Human studies in English in MEDLINE, Current Contents, BIOSIS, Science Citation Index, and the popular media (including a LEXIS-NEXIS search and information from the World Wide Web and lay media) for 1966 to July 1999 using the search terms creatine, creatine supplement#, creatine monophosphate, and creatine NOT kinase. DATA SYNTHESIS: Creatine use is common among professional athletes. Its use has spread to college athletes, recreational athletes, and even children. Most creatine supplement regimens include a loading dose of 20 to 30 grams divided in 4 equal doses for 5 to 7 days, followed by a 2 gram per day maintenance dose. The increased creatine in the muscle may allow larger stores of phosphocreatine to build, and provide extra energy in the form of adenosine triphosphate. Despite the many clinical trials, high-quality research is lacking. Laboratory investigations of endurance isotonic exercises, strength and endurance during isotonic exercises, isokinetic torque, isometric force, and ergometer performance have yielded roughly an equal number of published studies showing a positive effect or lack of effect. Field studies (i.e., on subjects participating in sports activities) are less impressive than laboratory studies. Performance was more often improved for short-duration, high-intensity activities. Reports have linked creatine to weight gain, cramping, dehydration, diarrhea, and dizziness. Creatine may decrease renal function, but only two case reports of this effect have been published. Creatine appears to be well tolerated in short-term trials.
CONCLUSION: While creatine may enhance the performance of high-intensity, short-duration exercise, it is not useful in endurance sports. Because commercially marketed creatine products do not meet the same quality control standards of pharmaceuticals, there is always a concern of impurities or doses higher or lower than those on the labeling. Consumers should balance the quality of information supporting the use of creatine with the known and theoretical risks of using the product, including possible renal dysfunction.