Ever ask your teenage son what’s he buying at the local health-food store — or ordering online?

You may want to find out. More than one in 10 teen boys and more than one in five male high school athletes are using muscle-building products, according to a new study — despite ongoing recommendations that they steer clear.

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Creatine is one of the most popular weight-gain supplements among boys 13 to 18 years old, despite warnings about its use and the long-term health risks of the supplements.

Risks of creatine include liver and kidney damage, dehydration, and muscle cramps. Testosterone, which is also often used, is tied to liver and kidney impairment and may even halt bone growth.

Almost 75 percent of sales attendants said a 15-year-old was allowed to purchase creatine.

Both supplements are legal, but age restrictions should be listed on the labels.

To find out how often the products were being sold to minors, researchers posed as 15-year-old high school athletes and contacted 244 health-food stores across the United States via telephone.

Sales attendants were asked what supplements they might recommend for someone trying to increase muscle strength. If a sales attendant did not mention creatine or testosterone boosters initially, each of these supplements was then specifically mentioned. The salespeople were also asked if a 15-year-old could purchase these products on his own in the store.

Just over 67 percent of sales attendants recommended creatine without a prompt; nearly 10 percent of sales attendants recommended a testosterone booster. Regarding availability, almost 75 percent of the sales attendants who were contacted stated a 15-year-old was allowed to purchase creatine, while 41 percent stated one could purchase a testosterone booster.

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The results have the American Academy of Pediatrics again asking doctors to talk with teenage patients, especially athletes, about safe, healthy methods to improve athletic performance. The organization is also encouraging retailers and state legislatures to consider banning the sale of these products to minors.

Parents should also pay attention when kids search for information about these products online, and be aware of pressures teen athletes may face to bulk up or use performance-enhancing products.

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“With our high school athletes, I tell them to be very cautious about what they get, particularly the boys,” said Dr. William Kelton Vasileff, a sports medicine orthopedic surgeon at The Ohio State University Wexner Medical Center. “They want to get stronger, but they have to be very careful what they’re putting in their body.”

Vasileff told LifeZette he routinely recommends for his athletes “not a lot of junk food or sugar, not a lot of pop. I tell them, ‘You don’t need Gatorade all the time — it’s got a ton of sugar in it. And you don’t necessarily need all these different supplements.’ There are some things in those pre- and post-workout products — we don’t know exactly what they are or where they come from. I’m more of an ‘eat whole, good food’ kind of person. That’s worked for a couple thousand years.”