Creatine is a nitrogenous organic acid that occurs naturally in vertebrates and helps to supply energy to all cells in the body, primarily muscle. This is achieved by increasing the formation of Adenosine triphosphate (ATP). Creatine was identified in 1832 when Michel Eugène Chevreul discovered it as a component of skeletal muscle, which he later named creatine after the Greek word for meat, κρέας (kreas). In solution, creatine is in equilibrium with creatinine.
Creatine is naturally produced in the human body from amino acids primarily in the kidney and liver. It is transported in the blood for use by muscles. Approximately 95% of the human body's total creatine is located in skeletal muscle.
Creatine is not an essential nutrient, as it is manufactured in the human body from L-arginine, glycine, and L-methionine.
In humans and animals, approximately half of stored creatine originates from food (mainly from meat). A study, involving 18 vegetarians and 24 non-vegetarians, on the effect of creatine in vegetarians showed that total creatine was significantly lower than in non-vegetarians. Since vegetables do not represent the primary source of creatine, vegetarians can be expected to show lower levels of directly derived muscle creatine. However, the subjects happened to show the same levels after using supplements. Given the fact that creatine can be synthesized from the above mentioned amino acids, protein sources rich in these amino acids can be expected to provide adequate capability of native biosynthesis in the human body.
Creatine supplements are sometimes used by athletes, bodybuilders, wrestlers, sprinters and others who wish to gain muscle mass, typically consuming 2 to 3 times the amount that could be obtained from a very-high-protein diet. A survey of long-term use gives the creatine content of several foods. The Mayo Clinic states that creatine has been associated with asthmatic symptoms and warns against consumption by persons with known allergies.
While there was once some concern that creatine supplementation could affect hydration status and heat tolerance and lead to muscle cramping and diarrhea, recent studies have shown these concerns to be unfounded.
There are reports of kidney damage with creatine use, such as interstitial nephritis; patients with kidney disease should avoid use of this supplement. In similar manner, liver function may be altered, and caution is advised in those with underlying liver disease although studies have shown little or no adverse impact on kidney or liver function from oral creatine supplementation. In 2004 the European Food Safety Authority (EFSA) published a record which stated that oral long-term intake of 3g pure creatine per day is risk-free. The reports of damage to the kidneys by creatine supplementation have been scientifically refuted.
Long-term administration of large quantities of creatine is reported to increase the production of formaldehyde, which has the potential to cause serious unwanted side-effects. However, this risk is largely theoretical because urinary excretion of formaldehyde, even under heavy creatine supplementation, does not exceed normal limits.
Extensive research over the last decade has shown that oral creatine supplementation at a rate of 5 to 20 grams per day appears to be very safe and largely devoid of adverse side-effects, while at the same time effectively improving the physiological response to resistance exercise, increasing the maximal force production of muscles in both men and women