Creatine

• Creatine monohydrate contains 88% creatine and 12% water. A 5 gram dose of creatine monohydrate provides 4.4 grams of creatine.
• Creatine phosphate is 62.3% creatine and 37.7% water. A dose of creatine phosphate provides less creatine than an equivalent dose of creatine monohydrate, plus creatine phosphate is generally more expensive.
• Creatine citrate is more water soluble, but contains only 40% creatine and is more expensive. Creatine monohydrate is by far the most popular form of this supplement.
  
  Absorption
  Creatine is readily absorbed from the stomach.
  
  Dietary Sources
  Animal protein is the best source of dietary creatine.
  
  

Creatine is found in the body in muscle, brain, and blood. However, most creatine in the body is stored in muscles, where it is found in two forms. About 40 percent exists as free creatine while approximately 60 percent is phosphorylated in a form known as phosphocreatine. Creatine is converted in the body to creatine phosphate, which is a storage form of high-energy phosphate used for rapid regeneration of ATP. Creatine is used by the body to recycle adenosine diphosphate (ADP) to adenosine triphosphate (ATP). ATP is stored in the mitochondria of muscle cells and produces energy when converted into ADP. Muscle fatigue occurs when the supply of ATP runs low. Creatine helps the body to convert ADP to ATP, providing more energy to the muscles. This allows the muscles to do more work and be less susceptible to fatigue.

Studies report that creatine supplementation can result in increased power and strength, improved performance times, and increased muscle mass. Creatine is currently a legal method of enhancing performance and increasing body mass. At the 19th Annual Southwest American College of Sports Medicine Meeting, two long-term creatine studies were presented by the Exercise & Sport Nutrition Lab at the University of Memphis. Both studies reported that nine months of creatine supplementation (average dose of 5 grams per day) in athletes had no negative effects on markers of renal function(5) or muscle and liver enzymes(6) in comparison to athletes not taking creatine.

Concern does exist regarding the use of creatine. French authorities are so concerned about the safety of creatine that they have made the sale of creatine supplements illegal. Furthermore, in January 2001, France's Food Safety Agency posted warning statements regarding creatine on the Agency's WEB site. Their position is that the risks associated with taking creatine are "currently insufficiently evaluated," and that, in addition to other known side effects, long-term supplementation may present "a potential carcinogenic risk."(7) However, it is noted that a Medline search did not produce studies that linked the use of creatine with cancer or increased cancer risk.

Two surveys that show substantial numbers of high school athletes are using creatine supplementation. In one survey 16% of the athletes from 11 high schools in Tennessee admitted to using creatine;(8) in another survey, 44% of the high school athletes from a single school in a suburb of New York City reported using creatine.(9) Experts strongly recommend against the use of creatine among adolescent athletes until more is known about its safety.

Topics that warrant evaluation include creatine's influence on insulin production, feedback inhibition of endogenous creatine synthesis, and contaminants that occur in products as a result of manufacturing procedures.(10)

Creatine increases both the body's overall water content and its ratio between intracellular and extracellular water. Strenuous exercise causes water loss from the extracellular space. If creatine has already caused a shift or buildup of water in intracellular spaces, an imbalance may occur. Thus, strenuous exercise can make an individual dehydrate faster, which can contribute to heat stroke and cramping due to loss of water in the extracellular space.

Although only a couple of cases have been reported, large doses of creatine coupled with intense exercise can lead to kidney dysfunction.(11, 12) Excess creatine is excreted through the kidneys. To reduce kidney burden, suggest increased fluid intake in order to dilute the contents and facilitate elimination.

Another potential problem associated with creatine use is related to possible contaminants that are produced during the manufacture of the product. Creatine is produced from sarcosine and cyanamide. This process results in the generation of variable amounts of contaminants such as dicyandiamide, dihydrotriazine, and creatinine.(12) Consumers should be advised of this and realize that consumption of large doses of creatine also increases the level of ingested contaminants. However, some companies state on their labels that their creatine products are guaranteed to be free of these contaminants. Until further toxicological studies are conducted, the effects of these contaminants are not fully understood. Also, an additional concern in Europe about creatine products has to do with the fact that the amino acid sarcosine, which is used in the production of creatine, could originate from bovine sources.

Health Conditions
Since excess creatine is excreted through the kidneys, hypertensive individuals should use caution due to fluid retention and potential increased stress on kidney function.

Side Effects
Reports have linked creatine to weight gain, cramping,(13) dehydration, diarrhea, dizziness, and on rare occasions, kidney problems. To avoid diarrhea, limit doses to no more than 5 grams per serving.