Does oral creatine supplementation improve strength? A meta-analysis
- 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 An expert in the field was contacted for sources of unpublished data.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.
This meta-analysis has some limitations. Our definition of strength included only “pure strength” or “power” measurements to allow statistical comparisons between similar outcomes. Because muscle strength is related to muscle endurance, researchers may define strength differently. It is not obvious at what point an exercise becomes a test of endurance and not just strength, but there is a physiologic basis for believing that creatine supplementation would more markedly improve performance in maximal or shorter duration exercises (ie, requiring strength and not endurance). The inclusion criteria for this project were determined before study review and selection and were applied consistently across all studies.
The quality and design of identified studies was another limitation. Most were small and did not fully delineate their randomization or blinding strategies. Multiple variations in study protocols made combining results of different studies somewhat problematic. Unfortunately, meta-regression or subanalysis for variables such as concurrent resistance training, previous training level, age, and sex were not possible because too few studies evaluated these variables independently of one another. Almost all of the studies finding a benefit of creatine supplementation were in young, previously trained men who engaged in resistance training concomitantly with supplementation, and the outcome measured was maximal weight lifted. Those studies not finding a difference were generally of less highly trained or older individuals, did not include resistance training, and more often investigated outcomes other than maximal weight lifted. This meta-analysis identifies that it is impossible to conclude from the existing literature which combination of variables is necessary to see a benefit of creatine supplementation.
More information is needed on the safety of creatine supplementation. Although a recent review35 reported no significant short-term adverse effects, no adequate long-term studies have been conducted. Two retrospective trials36,37 reported no adverse effects from longer-term (up to 5 years) creatine supplementation;however, neither study was randomized, blinded, or controlled, and neither had sufficient statistical power to detect uncommon adverse effects. Additionally, the designs of these studies precluded the possibility of detecting serious adverse effects such as death or disability. There have been case reports of renal dysfunction due to creatine38-40 and, as of 1998, the Food and Drug Administration had received 32 adverse event reports including seizures, myopathy, rhabdomyolosis, cardiac arrhythmia, and death.41
Given the popularity of nutritional supplements among all levels of athletes, clinicians cannot avoid questions about the effectiveness and safety of creatine supplementation. This meta-analysis demonstrated that oral creatine does improve performance during maximal resistance exercises in young men. However, we found no benefit for outcomes other than maximal weight lifted, suggesting that creatine may not improve actual performance in more complex movements requiring strength, speed, and coordination of multiple muscle groups. Studies investigating the effect of creatine in actual athletic performance are lacking.
Several important questions remain to be answered about creatine. What are the effects for women and older individuals? Is resistance training necessary to see strength performance improvement? Are these improvements in strength accompanied by improved athletic performance? How long do the effects of creatine remain after discontinuing supplementation? Most importantly, what is the long-term safety profile of creatine? Without further research to answer these questions, we cannot support the use of creatine supplementation for performance enhancement despite evidence for a positive impact on some components of strength.
Drug therapy for prevention and treatment of postmenopausal osteoporosis
| Drug (trade name) | Indication and dosage | Possible side effects (% of patients) | Cost per month* |
|---|---|---|---|
| Calcium and vitamin D (generic,Tums,Citracal, and others) | Prevention and treatment: 1200 –1500 mg/day calcium and 800 IU/day vitamin D | Nausea,dyspepsia (uncommon), constipation (10%) | $5 (both) |
| Estrogen †(Premarin,Ogen,Estrace, Estraderm,and others) | Prevention: 0.625 mg/day conjugated equine estrogen or the equivalent;0.3 mg/day may be effective | Nausea,breast tenderness, vaginal bleeding, mood alterations, headache, bloating | $14 –$28 |
| Alendronate (Fosamax) | Prevention:5 mg/day or 35 mg/week Treatment:10 mg/day or 70 mg/wk | Nausea, dyspepsia, esophageal irritation | $67 |
| Risedronate (Actonel) | Prevention and treatment: 5 mg/day or 35 mg/week | Abdominal pain, esophageal irritation | $67 |
| Raloxifene (Evista) | Treatment: 60 mg/day | Hot flashes (6%), leg cramps (3%) | $70 |
| Calcitonin nasal spray (Miacalcin) | Treatment:200 IU/day (1 spray in 1 nostril per day) | Rhinitis (5%), epistaxis, sinusitis | $66 |
| *Average wholesale cost to the pharmacy for 30 days of therapy; (Drug Topics Red Book. Montvale, NJ; Medical Economics Co., Inc, 2002.) | |||
| †Women with a uterus need to take a progestin such as medroxyprogesterone acetate (Provera $30/month, generic $9/month) or a combination estrogen/progestin product (Prempro $33/monh, FemHRT $26/month). | |||
On page 868 of the October issue a name was misspelled; the correct name is Brian S. Alper.
In the table appearing on page 877 of the October issue, the entry for Fosamax inadvertently combined prevention and treatment dosages. The corrected entry is shown below.
· Acknowledgments ·
