Many nutritional supplements, and the accompanying health or performance claims, come and go without much excitement. But none has created the amount of interest and debate as creatine. Proponents advocate creatine as a safe and effective supplement to enhance physical performance. Opponents contend that it is harmful. Rumor and conjecture fuel the controversy. The enthusiasm surrounding creatine is bolstered by professional athletes who provide testimonials that their success is supported by this small protein.
The scientific basis for creatine supplementation is linked to this protein’s role as an immediate source of energy for working muscles. A modified form of creatine, phosphocreatine, is the key player in the transformation of energy from food into the common chemical form of energy that all cells use. In contrast to other chemical forms of energy in cells, phosphocreatine levels can be stockpiled, thus increasing the amount of energy available to working cells in muscles and other tissues in the body.
People either consume creatine directly from meat, fish and poultry or they make it from other proteins in the diet--but only in small amounts. A normal dietary intake of creatine is about 1 gram per day. Two pounds of raw steak contains 4 grams of creatine. The blood transports creatine to the cells, where it is stored as phosphocreatine. Muscles, nerves and the heart contain more than 95 percent of all creatine and phosphocreatine in the body.
Taking creatine supplements markedly increases these levels in the muscles. People who supplement may take anywhere from 10 to 20 grams per day for periods ranging from 4 to 6 days. This regimen is termed "creatine loading"; it can raise muscle creatine and phosphocreatine concentrations by more than 20%.
The benefits of supplementation on performance are limited to specific types of activities. Preliminary information suggests that high- intensity, short duration or stop and go activities may benefit from creatine supplementation. Some examples include weight training, baseball, sprinting, throwing, jumping, football, and soccer. However, only people with low levels of muscle creatine will benefit from creatine supplementation.
In contrast to high-intensity or anaerobic activities, creatine supplementation does not improve, and may even worsen, endurance performance. One study found that marathon runners had poorer performances after creatine loading.
There is one consistent side effect of creatine supplementation - a small weight gain, most likely from water accumulation. There are anecdotal reports of other side effects, including kidney and liver damage, muscle cramps during exercise in the heat and increased number of muscle strains and pulls.
Future studies need to address some practical issues. These issues include development of safe and effective programs to maximize muscle creatine accumulation and to maintain elevated creatine stores, determination of long term side effects of creatine supplementation, and assessment of its effects in women and the elderly. One promising area is the use of creatine supplementation to restore muscle function in patients with muscle loss and specific types of nerve and muscle diseases.