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Creatine

Pronunciation
Scientific names: Methylguanidine acetic acid, N-amidinosarcosine

Efficacy-safety rating:

ÒÒ...Ethno or other evidence of efficacy.

Safety rating:

...Little exposure or very minor concerns.

What is Creatine?

Creatine is acquired through the diet or is synthesized by the body. It is a constituent of muscle tissue and occurs naturally in meat, fish, and other animal products, with trace amounts found in milk and some plants. Herring contains 6.5 to 10 g/kg of creatine, while beef, pork, salmon, and tuna all contain approximately 4 to 5 g/kg. A typical western diet provides 1 to 2 g/day; vegetarians consume much less and thus, their daily creatine needs are met completely by their bodies' synthesis from arginine and glycine by 2 enzymatic reactions. In the kidney, guanidinoacetic acid is produced and upon transfer to the liver, is methylated using methionine to form creatine. This process produces approximately 1 to 2 g/day of creatine. Creatine is then transported via circulation to various tissues, in particular skeletal muscle, for utilization.

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The majority of studies evaluating the effects of oral creatine supplementation have been conducted using creatine monohydrate powder. The effects of other supplement formulations, such as creatine citrate or creatine phosphate, have not been determined. Creatine monohydrate is available in several dose forms, including bar, candy, capsules, gel, gum, liquid, and powder. The efficacy of some of these dose forms has not been demonstrated.

What is it used for?

Traditional/Ethnobotanical uses

Creatine was discovered in 1832 by the French chemist Michel Chevreul as an organic constituent of meat. Muscle work was later associated with creatine in 1847 when it was observed that the flesh of wild foxes killed in the chase contained 10 times more creatine than those living in captivity. In 1911, creatine was reported to be involved in muscle metabolism; it was demonstrated that oxygen consumption could be stimulated by adding creatine to muscle mince. In the early 1930s, it was suggested that creatine phosphate might serve as the source of energy for muscle contraction when its large free energy of hydrolysis (12 kcal/mol) was identified. By 1939, oxygen consumption was shown to be coupled to creatine phosphate synthesis in muscle, which confirmed that oxidative phosphorylation was indeed a function of creatine.

In the late 1960s, researchers began using needle biopsy techniques to study the breakdown and resynthesis of adenosine triphosphate (ATP) and creatine phosphate with exercise. It was not until the early 1990s that creatine's influence on exercise performance in humans began to be studied. Reports followed in 1992 of a 20% increase in human muscle mass subsequent to creatine supplementation. Numerous studies have since been conducted in untrained or moderately trained subjects in the laboratory setting to determine the potential ergogenic value of creatine supplementation. Benefit has extended beyond simple laboratory exercises, with enhanced sprint and weight-lifting performance reported in elite athletes.

General uses

Limited trials have shown creatine to enhance performance of short-duration, high-intensity exercise. A systematic review provided evidence for a beneficial effect in various muscular dystrophies, but the data do not demonstrate the same positive effect in patients with metabolic myopathies. Preliminary data suggest that creatine may be beneficial in neurodegenerative diseases, such as amyotrophic lateral sclerosis and Huntington and Parkinson diseases, but larger clinical studies are required to confirm this benefit. Case reports show benefits of creatine supplementation in 2 of the 3 creatine deficiency syndromes identified, and it is hypothesized that these 2 syndromes may be partly or completely cured by early and long-term creatine supplementation. More clinical trials are needed to confirm this effect.

What is the recommended dosage?

Oral doses range from 2 to 35 g daily. Loading doses are usually 20 g/day for up to 1 week, and maintenance doses are 5 g/day.

How safe is it?

Contraindications

Patients with a history of kidney dysfunction or diabetes, or those taking concomitant nephrotoxic agents should avoid creatine supplementation or be monitored closely if supplementation is necessary.

Pregnancy/nursing

Information regarding safety and efficacy in pregnancy and lactation is lacking.

Interactions

None well documented.

Side Effects

Most reports of adverse reactions remain anecdotal because they lack documentation in well-controlled trials. The only well-documented adverse reaction is an increase in body mass. Anecdotal reports include minor GI upset, dehydration, heat-related illnesses, reduced blood volume, electrolyte imbalances, and muscle cramping.

Toxicities

Research reveals little or no information regarding toxicology with the use of this product.

References

  1. Creatine. Review of Natural Products. Facts & Comparisons 4.0. October 2008. Accessed October 14, 2008.

Copyright © 2009 Wolters Kluwer Health

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