Creatine in the Human Body
Creatine is an endogenous (made by the body) substance that is present in every human cell. It functions as an energy storehouse. Creatine is required for physical and mental exertion.
In the body, creatine is synthesized from the amino acids glycine, arginine, and methionine, primarily in the liver, kidneys, and pancreas, and it is transported from there to all the cells in the body via the bloodstream. Since creatine is involved in all processes that require energy, muscle, brain and nerve cells receive correspondingly larger amounts.
The creatine reserves of a person who weighs 70 kg equal about 120 grams. The vast majority of creatine (app. 95%) is stored in the skeletal muscles. Creatine is primarily involved in muscle contraction. It is taken up from the blood into the cell membrane by means of a sodium-dependent creatine transporter.
Approximately 60-70% of the total creatine in muscle is stored in the form of the highenergy molecule phosphocreatine. The remaining 30-40% is present in the form of free creatine. Besides adenosine triphosphate, phosphocreatine is the most important source for energy in the body. All of the body’s cells can use only adenosine triphosphate (ATP) as an energy-releasing substance. Since the ATP reserves in the body are limited, ATP has to be continuously resynthesized. ATP is produced from the energy sources fat and carbohydrates over a fairly long time frame.
If a cell needs energy, the “high-energy” ATP is converted to “low-energy” adenosine diphosphate (ADP). Similar to a battery, creatine (phosphocreatine) charges low-energy ADP up to high-energy ATP until ATP that has been converted from fat and carbohydrates is available.
Muscles contain 3-4 more phosphocreatine than ATP, and the phosphocreatine serves as a short-term energy reserve for the times when the need for ATP is greater than the synthesis of ATP from carbohydrates and fat can provide. Phosphocreatine levels and the regeneration of ATP play key roles when the body is involved in intense, repetitive forms of exertion. Increasing the amount of creatine and phosphocreatine speeds up the regeneration of ATP, which leads directly to the release and availability of more energy.
Creatine supplementation increases the amount of creatine in muscle tissue
Orally administered creatine is absorbed by the intestines and then goes into the bloodstream. Small doses of creatine result in maximum blood plasma concentrations after fewer than two hours.
For concentrations of creatine in muscles there appears to be an upper limit that can not be extended (~160 mmol per kg muscle dry matter). Ongoing supplementation with large amounts of creatine oes not raise the levels of creatine in muscle any more, so is not recommended.
Diagram 1: Endogenous Creatine Synthesis and Creatine Metabolism.
Diagram 2: Creatine is involved in the regeneration of the body’s energy source ATP.
Diagram 3: Bioavailability of Creapure®
One-time administration of Creapure® (5 g dissolved in 450 mL water) results in markedly elevated blood plasma creatine levels. Creatinine levels do not go up