Creatine

Creatine is a nitrogenous organic acid that occurs naturally in vertebrates and helps to supply energy to muscle and nerve cells. 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 flesh, Kreas.
Creatine functions with the enzyme creatine kinase. The presence of this energy buffer system keeps the ATP/ADP ratio high where ATP is needed, which ensures that the free energy of ATP remains high and minimizes the loss of adenosine nucleotides, which would cause cellular dysfunction. The phosphocreatine/creatine kinase system also acts as an energy transport system from those places where ATP is generated (mitochondria and glycolysis) to those places where energy is used.
In humans, about half of the daily creatine is biosynthesised from three different amino acids - arginine, glycine, and methionine. The rest is supplied by dietary sources. 95% of creatine is later stored in the skeletal muscles.
Short-term use of creatine in healthy people is generally considered safe. Continuous intake of excessively high dosages of creatine may lead to any of several possible side effects. Consistently high doses could lead to hypertension due to increased water retention, for example.
Creatine supplementation utilizing proper cycling and dosages, however, has not been linked with any adverse side effects beyond occasional dehydration due to increased muscular water uptake from the rest of the body.
According to the opinion statement of the European Food Safety Authorities (EFSA) published in 2004 it was concluded that "The safety and bioavailability of the requested source of creatine, in foods for particular nutritional uses, is not a matter of concern provided that there is adequate control of the purity of this source of creatine (minimum 99.95%) with respect to dicyandiamide and dihydro-1,3,5-triazine derivatives, as well as heavy metal contamination. The EFSA Panel endorses the previous opinion of the SCF that high loading doses (20 gram / day) of creatine should be avoided. The Panel considers that the consumption of doses of up to 3g/day of supplemental creatine, similar to the daily turnover rate of creatine, is unlikely to pose any risk".
This opinion is corroborated by the fact that creatine is a natural component in mothers' milk and that creatine is absolutely necessary for brain development in the human embryo and the baby, as well as for optimal physiological functioning of the adult human body, especially the brain, nervous system, the muscles and other organs and cells of high energy expenditure, where the creatine kinase (CK) system is highly expressed and creatine levels are high.
Since vegetables do not contain creatine, vegetarians clearly show lower levels of muscle creatine which, upon creatine supplementation, rise to a level higher than in meat-eaters.
Creatine supplementation has been, and continues to be, investigated as a possible therapeutic approach for the treatment of muscular, neuromuscular, neurological and neurodegenerative diseases. These studies appear to have had positive results.