WATERLOO - Adults often say if they could bottle the energy of children and sell it, they would.

In the world of mass marketing, it's no surprise that someone has.

Red Bull, Amp, Adrenaline Rush, Lost Energy, Full Throttle and scores of other so-called energy drinks are a million-dollar market, padding the pockets of their makers and revving up the consumers who drink them.

But health experts say the canned energy should be off limits for kids.

"As a physician, I don't recommend them for children," said Dr. Ronald Flory, a family practitioner at Covenant Clinic. "There are a number of health-related concerns."

A survey by an Australian consumer group showed 27 percent of 8- to 12-year-old boys, 12 percent of 8- to 12-year-old girls, 24 percent of 12- to 18-year-old boys and 20 percent of 12- to 18-year-old girls had had at least one energy drink in the two weeks prior to the survey.

In the United States, where health officials are struggling with a growing childhood obesity epidemic, the calorie count in energy drinks amounts to more bad news. Red Bull's 8-ounce can contains 110 calories. Hansen's Energy Pro packs 120 calories in its 8-ounce can.

"Calories in fluids is a very major player in weight gain," said Flory.

Also of concern is the caffeine content in energy drinks. Caffeine does provide a quick energy boost, but it doesn't come without a cost, especially in children. It can cause sleeplessness, nervousness and irritability.

In 2002, Australia began requiring a warning label on energy drinks: "This food is not recommended for children, pregnant or lactating women and individuals sensitive to caffeine."

"A can of Red Bull has two times the amount of caffeine as a can of Coke," said Lori Fincher, a dietitian at Allen Hospital. "They'll be bouncing off the walls. It gives them a quick, high buzz and makes them feel like they have all this energy."

But caffeine also is a diuretic that can quickly rob kids of fluids, leaving them dehydrated, said Fincher. It also elevates blood pressure and speeds the heart rate. This is of special concern for young athletes.

"It will enhance concentration and performance, but it can interfere with the appropriate fluid balance and enhances the chances of heart rhythm disturbance," said Flory.

A handful of people suffer from a heart valve problem that can go undetected until, under a combination of excess caffeine, weather conditions and a stressful workout, it causes them to collapse on the field.

"It is rare, but it can happen," noted Flory.

The ingredients in energy drinks sometimes include the stimulant ephedrine. Combined with caffeine, ephedrine has been proven to cause deadly heart problems.

High school officials in Burbank, Calif., banned energy drinks in 2000 when two student athletes who had consumed drinks with ephedrine fainted.

Taurine, an ingredient which, at high levels, is said to boost the effects of stimulants, is a common ingredient in many energy drinks, as is guarana or extracts from its seeds, yet another source of caffeine.

Dr. Michael Hirt, medical director at the Center for Integrative Medicine at the Encino-Tarzana (Calif.) Regional Medical Center, worries about the effects of the concoctions.

"It just becomes more of a witches brew. You're playing with things that we don't really understand and the long-term consequences are unclear," he said in an Associated Press story.

Contact Meta Hemenway-Forbes at (319) 291-1483 or meta.hemenway-forbes@wcfcourier.com.