Creatine and creatinine are chemicals found inside cells. Certain foods contain creatine, and it is also available to buy at health food stores. Creatine helps cells to function and is metabolized into creatinine. The creatinine can be measured in the blood, and its levels can change in some disease states.
Sources
Creatine is naturally high in animal meat such as beef. Fish such as tuna and salmon have high levels of creatine as well. In addition to food sources, supplements are available from nutrition stores, typically as creatine monohydrate. If dietary sources are insufficient to meet the body's needs, creatine can be synthesized by the kidneys and liver from amino-acids, which are the building blocks of protein, as noted by "Guyton and Hall Textbook of Medical Physiology," by John Hall, Ph.D.
Function
If levels of creatine are adequate in the body, cells, particularly muscle cells, can use the chemical to regenerate adenosine triphosphate, or ATP. ATP is a chemical that carries three phosphate groups that are used to store and transfer energy. For example, ATP is used to make muscles contract. In so doing, the ATP loses a phosphate group, so it has only two phosphates and is called ADP for adenosine diphosphate. Creatine is important because it is able to rapidly regenerate ATP by donating a phosphate to ADP. Therefore, creatine helps the cells utilize energy, according to "Harrison's Principles of Internal Medicine."
Metabolism
Creatine is synthesized from methionine, glycine and arginine. Creatine spontaneously breaks down into the chemical creatinine. Creatinine levels are frequently measured in blood tests called metabolic profiles, according to the "Guyton and Hall Textbook of Medical Physiology."
Role in Disease
Problems in creatine metabolism are associated with muscular problems. In addition, since creatinine is filtered from the blood into the urine by the kidneys, creatinine levels are indicative of kidney disease. Higher levels of creatinine in the blood generally indicate kidney dysfunction, according to "Harrison's Principles."
Role in Exercise
A study in "The Journal of Family Practice" titled "Does oral creatine supplementation improve strength? A Meta-analysis," concluded that creatine supplementation with resistance training in men younger than age 36 can increase the maximum weight lifted. These findings were not observed in older men and women. In addition, studies have not supported a role for creatine in the improvement of endurance exercise. Creatine should not be used in those with kidney disease, as it can speed the progression.
References
- "Guyton and Hall Textbook of Medical Physiology"; John E. Hall; 12th Ed 2010
- "Harrison's Principles of Internal Medicine"; Anthony Fauci et al; 17th Ed 2008
- "The Journal of Family Practice"; "Does oral creatine supplementation improve strength? A Meta-analysis."; Dempsey et al; November 2002
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