Some athletes think that "winning is everything," and take large doses of nutritional supplements to get an edge over their opponents. Creatine is the most popular sports supplement. Many athletes, including some children and adolescents, take creatine supplements to increase strength and improve sports performance.

Creatine is a natural source of energy for muscle contraction. The body produces creatine in the liver, kidneys, and pancreas. People can also get creatine by eating meat or fish. (Vegetarians may have lower amounts of creatine in their bodies.) Most of the creatine in the body is stored in skeletal muscle and used during physical activity. The rest is used in the heart, brain, and other tissues.

Taking creatine supplements may increase the amount of creatine in the muscles.

Muscles may be able to generate more energy or generate energy at a faster rate.

Some people think that taking creatine supplements along with training will improve performance by providing quick bursts of intense energy for activities such as sprinting and weightlifting.

Vegetarians and other individuals with lower amounts of natural creatine may see more of a difference by taking creatine supplements, compared with other people. There may be a "saturation point" that limits how much creatine muscles can store.

Creatine supplements come in a wide variety of brand names and products. The supplements are available over the counter at vitamin, drug, and grocery stores, and on the Internet.

Use of creatine supplements is widespread and is expected to rise. Most of the people who use creatine supplements are:

• Male
• Athletes in power sports, such as football, wrestling, hockey and bodybuilding
• Athletes at all levels of performance, from professional to amateur, college, high school, and middle school.

A study by the American Academy of Pediatrics of middle-school and high-school students ages 10 to 18 years found creatine use in all grades 6 through 12. About 5.6% of the study participants and 44% of high-school senior athletes admitted taking creatine.

Another study by the Blue Cross and Blue Shield Association found an estimated 1 million young people ages 12 to 17 years have taken performance-enhancing sports supplements. Use of supplements was reported by 5% of participants.

It is important to remember that, although creatine is a "natural" product, it is not always safe to take creatine supplements. The U.S. Food and Drug Administration does not regulate nutritional supplements. This means that the creatine products available in stores may vary in amount and quality, and there is no guarantee of safety or purity.

According to a study by the Mayo Clinic, many young athletes who take creatine supplements rely on the advice of friends, not doctors. Some creatine users do not know how much creatine to take and may take more than they should.

People who take creatine supplements may gain weight because of water retention in the body's muscles. Other side effects of long-term use of creatine supplements include muscle cramps, dehydration, diarrhea, nausea, and seizures.

It may be dangerous to take creatine supplements while undergoing dehydration (for example, for wrestling competition) or when trying to lose weight.

Doctors do not know the effects of creatine supplements on important organ systems, such as the heart, brain, kidneys, liver, and reproductive organs, or the effects of combining creatine supplements with over-the-counter medications, prescription drugs, and vitamins.

Medical researchers are studying the safety and effectiveness of creatine supplements. They also are studying whether creatine supplements may help in the treatment of diseases that cause muscles to shrink and fail, such as heart failure/disease, muscular/neuromuscular diseases, and stroke.

Although research is underway, doctors do not know the long-term health effects of taking creatine supplements, especially in children who are still growing. Because of these unknown risks, children and adolescents younger than 18 years and pregnant or nursing women should never take creatine supplements. People with kidney problems also should never take creatine supplements.

No matter what your age or health condition, always see your doctor for advice before taking creatine supplements.