Creatine is an amino acid that occurs naturally in the human body. The estimated daily need for creatine in humans is about two grams. The body produces 1-2 grams of creatine each day in the liver, kidneys, and pancreas. Additional dietary sources of creatine, primarily meats and fish, supplement the body's production of creatine. A half-pound steak contains about one gram of creatine.
Synthetic creatine is considered a dietary supplement.
Creatine is stored in the heart, brain, retina, and skeletal muscles, where it is critical for high-intensity muscle contractions. By enhancing ATP turnover, creatine functions as an energy reservoir during repetitive activities that require short bursts of explosive energy. Creatine delays fatigue in repeated bouts of all-out strength work or sprinting, and allows the body to sustain a high power output. According to the American College of Sports Medicine, creatine supplementation can improve performance in repetitive anaerobic exercises. There is no conclusive evidence that it helps in swimming, running, or a single sprint event.