Creatine is a naturally occurring amino acid (protein building block) that's found in meat and fish, and also made by the human body in the liver, kidneys, and pancreas. It is converted into creatine phosphate or phosphocreatine and stored in the muscles, where it is used for energy. During high-intensity, short-duration exercise, such as lifting weights or sprinting, phosphocreatine is converted into ATP, a major source of energy within the human body.
Creatine supplements are popular among body builders and competitive athletes. It is estimated that Americans spend roughly $14 million per year on creatine supplements. The attraction of creatine is that it may increase lean muscle mass and enhance athletic performance, particularly during high-intensity, short-duration sports (like high jumping and weight lifting).
However, not all human studies have shown that creatine improves athletic performance. Nor does every person seem to respond the same way to creatine supplements. For example, people who tend to have naturally high stores of creatine in their muscles don't get an energy-boosting effect from extra creatine. Preliminary clinical studies also suggest that creatine's ability to increase muscle mass and strength may help combat muscle weakness associated with illnesses such as heart failure and muscular dystrophy.
Although not all clinical studies agree, some conducted in both animals and people have shown that creatine supplements improve strength and lean muscle mass during high-intensity, short-duration exercises (such as weight lifting). In these studies, the positive results were seen mainly in young people (roughly 20 years of age). Most human studies have taken place in laboratories, not in people actually playing sports. Creatine does not seem to improve performance in exercises that requires endurance (like running) or in exercise that isn't repeated, although study results are mixed.
Although creatine is not banned by the National Collegiate Athletic Association (NCAA) or the International Olympic Committee, using it for athletic performance is controversial. The NCAA prohibits member schools from giving creatine and other muscle building supplements to their athletes, although it doesn't ban athletes from using it. The French Agency of Medical Security for Food (AFSSA) asserts that the use of creatine supplements is "against the spirit of sportsmanship and fair competition."
Creatine appears to be generally safe, although when it is taken at high doses there is the potential for serious side effects such as kidney damage and the risk of inhibiting the body's natural formation of creatine.
Also of concern is the marketing of creatine-containing supplements directly to teens, with claims about changing one's body with little effort. One survey conducted with college students found that teen athletes frequently exceed the recommended loading and maintenance doses of creatine. Meanwhile, neither safety nor effectiveness in those under 19 has ever been tested.
A preliminary clinical study suggests that creatine supplements may help lower levels of triglycerides (fats in the blood) in men and women with abnormally high concentrations of triglycerides.
In a few clinical studies of people with congestive heart failure, those who took creatine (in addition to standard medical care) saw improvement in the amount of exercise they could do before becoming fatigued, compared to those who took placebo.