WASHINGTON (AP) - Kids who want to grow strong these days sometimes turn to creatine.

The strength training supplement, popular among pro and college athletes, has filtered down to the high school set. This unsettles adults, who doubt the young athletes understand what creatine does and don't know how many teens are involved.

``We do not know,'' said researcher Charles Yesalis of Penn State. ``I can speculate. I think a lot. I think it's down to the junior high level.''

Creatine is found almost entirely in skeletal muscle, where the compound helps to fuel the energy bursts needed for explosive contractions such as those in weight training.

Athletes take creatine supplements to give their muscles as much creatine as their cells can handle, expecting to gain extra energy, train longer and harder - and bulk up. And many studies have indicated creatine works. Athletes who take it get stronger and bigger, although some of the increased size may be the result of water retention.

Training with steroids produces greater strength gains, but the male hormone supplements are illegal for use as a training aid, not to mention potentially dangerous. Risks range from heart disease to baldness.

Creatine, on the other hand, is widely available and legal. The Food and Drug Administration lists it as a food supplement and allows it to be sold with no more restrictions than those on vitamins. Teen athletes can buy it at their local health food store - possibly their local supermarket.

Many teens do, but no one knows how many. Yesalis, who studies athletes' quests for better bodies through chemistry, would like government agencies such as the Centers for Disease Control and Prevention to add questions on substances such as creatine to their health habits surveys. Until national data are developed, the best researchers can get are ``tiny local studies,'' he said.

One new study is in the current issue of the Mayo Clinic Proceedings. Researchers had 182 male and 146 female Minnesota students ages 14 to 18 complete an anonymous questionnaire when they appeared for preparticipation physical exams that are required for sports.

Twenty-seven athletes, including one female, said they had used creatine, and 14 said they were using it at the time of the survey.

The researchers concede their survey of students who showed up for physical exams was not a random scientific sample. But they suspect it is still a valid snapshot. ``It's our impression that at least in terms of the Midwest, our athletes are reflective of the general population,'' said Dr. Jay Smith. Smith co-authored the article with fellow Mayo physician Diane L. Dahm.

The study found 74 percent of the young creatine users relied on their friends for information about the supplement. That's worrisome to Smith, who feels teens ought to go to adults who can give them more reliable information.

Teens should not use creatine, Smith said. ``The safest thing is not to take it,'' he said. Although short-term side effects are relatively mild, including cramping and diarrhea, long-term effects are not known because the substance has not been followed for long enough, he said.

It's not good for teens to become accustomed to using strength training supplements, Yesalis said. ``Speaking as a parent, I don't think we should get our kids in the habit,'' he said. ``When taken as directed, nothing there scares me. However, if there is one thing I have learned in 22 years, there is a group that lives by the adage that if one works, 10 will work great.''

The National Federation of State High School Associations, a governing body for high school sports, says high school officials, including coaches, should not condone supplement use.

However, another researcher, Richard Kreider of the University of Memphis, thinks the risks of creatine, even in high schoolers, are vastly overstated. Research has not found the stuff to be dangerous, and the cramping that is a commonly reported side effect can be controlled by drinking lots of water, he said.

Creatine may aid players, especially helping smaller teen athletes get stronger, play better and avoid being hurt in games against bigger opponents, Kreider said. And making creatine off-limits puts the supplement into the same general class as more dangerous substances, such as steroids, he said. Teen athletes may then say, ``I'm going to take the hard stuff that I'm also not allowed to take,'' he said.

Just the same, there should be limits, Kreider said. Teens who use the supplement should do so under supervision by coaches and parents, he said.

Copyright 2000 The Associated Press. All rights reserved.