Does oral creatine supplementation improve strength? A meta-analysis. (Original Research)

* OBJECTIVES Oral creatine is the most widely used nutritional supplement among athletes. Our purpose was to investigate whether creatine supplementation increases maximal strength and power in healthy adults.

* STUDY DESIGN Meta-analysis of existing literature.

* DATA SOURCES We searched MEDLINE (1966-2000) and the Cochrane Controlled Trials Register (through June 2001) to locate relevant articles. We reviewed conference proceedings and bibliographies of identified studies. An expert in the field was contacted for sources of unpublished data. Randomized or matched placebo controlled trials comparing creatine supplementation with placebo in healthy adults were considered.

* OUTCOMES MEASURED Presupplementation and postsupplementation change in maximal weight lifted, cycle ergometry sprint peak power, and isokinetic dynamometer peak torque were measured.

* RESULTS Sixteen studies were identified for inclusion. The summary difference in maximum weight lifted was 6.85 kg (95% confidence interval [CI], 5.24-8.47) greater after creatine than placebo for bench press and 9.76 kg (95% CI, 3.37-16.15) greater for squats; there was no difference for arm curls. In 7 of 10 studies evaluating maximal weight lifted, subjects were young men (younger than 36 years) engaged in resistance training. There was no difference in cycle ergometer or isokinetic dynamometer performance.

* CONCLUSIONS Oral creatine supplementation combined with resistance training increases maximal weight lifted in young men. There is no evidence for improved performance in older individuals or women or for other types of strength and power exercises. Also, the safety of creatine remains unproven. Therefore, until these issues are addressed, its use cannot be universally recommended.

* KEYWORDS Creatine; dietary supplements; meta-analysis. (J Fam Pract 2002: 51:945-951)

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KEY POINTS FOR CLINICIANS

* Oral creatine supplementation combined with resistance training increases maximal weight young men can lift.

* It is unknown whether this increase in strength translates into improvement in sports performance.

* Evidence in the existing literature is insufficient to draw" conclusions about the effect of creatine in women or older individuals.

* Because no long-term studies have been performed on the safety of creatine supplementation, its use should not be universally recommended.

Creatine has gained widespread popularity dining the past decade as a possible performance-enhancing agent among professional and recreational athletes. It is the most widely used performance enhancing supplement among youth aged 10 to 17 years, (1) with 15% to 30% of high school athletes (2,3) and 48% of male Division I college athletes (4) reporting creatine use. Considered a nutritional supplement, it is not regulated by the United States Food and Drug Administration nor is it banned by the International Olympic Committee or National Collegiate Athletic Association. Because of the widespread use of creatine, primary care providers must be knowledgeable about its effectiveness and safety.

Oral creatine monohydrate increases skeletal muscle creatine concentration by 16% to 50%, (5-7) but whether it is an effective ergogenic aid remains controversial. Multiple studies have investigated this question, but many have been small, often including fewer than 10 subjects, and results have been conflicting. Several reviews (8-14) have addressed the effectiveness of creatine, but there has not been a systematic and comprehensive meta-analysis to resolve the uncertainties...