Q. My son wants to play football, but he's smaller than the other boys. Is it safe for him to take a nutritional supplement such as creatine to increase his muscle?
A. Many teens, especially athletes, want to be bigger and stronger, and a fair number use creatine to do so. One study found that nearly 10 percent of high school boys have used it. Another study found that nearly half of college men have used it.
Creatine is sold as a supplement, but it is found naturally in the body, mostly in muscle. It increases the production of an "energy molecule" called adenosine triphosphate (ATP).
Creatine does not increase strength, but it may increase how well some athletes are able to train. There's some evidence that it can help young athletes build muscle mass. And it may improve athletic performance that requires short bursts of muscle activity, such as sprinting or weightlifting. These benefits are established mainly in younger men, and not in women or in older men. Also, there is no evidence that it helps athletes in endurance sports.
One problem with nutritional supplements such as creatine is that the U.S. Food and Drug Administration (FDA), which normally checks the safety of foods and medicines, does not check the safety of nutritional supplements. The FDA does not investigate to be sure the manufacturing process has prevented impurities from entering the supplement. There is little information on the short-term side effects -- particularly in children or teens.
Also, the immediate and long-term safety of creatine is not known. For that reason, creatine is banned by some sports organizations. Some reported side effects include muscle cramping, stomach pain, diarrhea, vomiting, rash, seizure, heart-rhythm problems and kidney problems.
Because of these side effects, and the fact that it is not a regulated substance, it is probably best that your son not use supplements. I'd say the best way for him to be athletic and at the top of his game is to stay healthy. Remind him to eat a well-balanced diet and exercise regularly. Make sure he is getting the amount of sleep he needs for his body to rest and grow.
He must also realize that he has not completed puberty yet and still has room to grow -- taller and wider. His muscles will bulk up naturally when he exercises, when the time is right for him.
Check in with his coach. Ask about suggestions for a weight-training program that might help him to get ready for football.
Even though you asked about your son, your question prompts me to mention one last thing. Some of my older patients have asked me about using creatine, along with exercise, to help fight the loss of muscle mass that comes with age. I tell them that I don't think there is good evidence that creatine has benefits for older people.
• Dr. Komaroff is a physician and professor at Harvard Medical School. Go to his website to send questions and get additional information: AskDoctorK.com.