Sean Morgart is a connoisseur of energy drinks, chugging them daily when he needs a boost and collecting rare brands when he travels.

But the 31-year-old father from South St. Paul has a different stance for his 8-year-old, who once asked to try one because it smelled like juice.

"Anything with caffeine," he said, "I try to keep that away from my daughter, period."

The tremendous growth in sales of energy drinks -- half of which are consumed by young adults or children -- has prompted a backlash from U.S. pediatricians and public health leaders. The latest warning, to be published Monday in the journal Pediatrics, concludes that energy drinks at best fail to live up to their hype and at worst present risks to children with heart conditions and other health problems.

Study authors from the University of Miami asked pediatricians "to be aware of the possible effects of energy drinks in vulnerable populations and screen for consumption to educate families."

Energy drinks are classified as dietary supplements, which exempts them from federal limits on caffeine content that apply to sodas, the study noted. Energy drinks contain 75 to 400 milligrams of caffeine -- more than a can of Mountain Dew, at 54 milligrams, and potentially more than a tall cup of Starbucks coffee. And while they boast natural stimulants such as taurine and guarana, doctors said their effects are unproven.

"What you're feeling is the caffeine and the sugar," said Dr. William Roberts, a sports medicine specialist at the University of Minnesota, who wasn't involved with the study. "I look at them as being more in the range of three to five cups of coffee, which is more stimulation than you need."

Young adults interviewed by the Star Tribune said they have tried energy drinks to stay up later, study longer and gain an edge in sports. Some said the benefits outweighed the bad taste of some brands, which drinkers described as cough syrup or "sour Mountain Dew."

"That to me is how effective the energy drink industry is at marketing," said Dr. Nimi Singh, who directs adolescent health and medicine at the University of Minnesota. "They're saying the payoff is worth it -- that you're going to get such a great result in your body that you can go ahead and drink this thing that almost tastes like medicine."

Students in David Ettesvold's health class in North St. Paul play video games all night and buy energy drinks to stay awake at school. If students bring them to his class, Ettesvold said he makes them read the ingredients aloud. Then he calculates their annual spending on the $2 to $4 beverages.

Ettesvold also sells bottled water for 25 cents, and tallies what students save by not buying sodas or energy drinks.

Casey Peterson drank energy drinks before 8 a.m. to prepare for high school mornings, only to feel groggy in the afternoons. A senior at the U of M, Peterson, 22, said he has reduced his intake to an occasional "quick aid" for studying. Mostly he avoids them.

"They make me crash," he said. "It's not worth it."

Unless they're mixed with alcohol. Peterson said he occasionally drank Four Loko or Sparks before the U.S. Food and Drug Administration took the combined alcohol-energy drinks off shelves last year. Bars still serve energy drinks as chasers, though, and young adults mix them with alcohol on their own.

At least one study has reported a rise in drunken young adults in emergency rooms, because energy drinks make them feel more alert than they really are, Singh said.

No worse than coffee?

In discouraging youth consumption, the Pediatrics study is taking on the prime market for energy drinks, which include Red Bull, Monster, Rockstar and Full Throttle.

Red Bull has advertised to teens through alignment with extreme sports and athletes such as snowboarder Shaun White, skier Lindsey Vonn and pitcher Tim Lincecum.

Responding to the Pediatrics study, the American Beverage Association said last week that risks from energy drinks are no greater than those from other beverages, and that coffeehouse coffee contains more caffeine than energy drinks.

Federal surveys have shown that teens get more caffeine from soda, tea or coffee than energy drinks, added the association's Dr. Maureen Storey.

Issues for athletes

The prospect that energy drinks improve athletic performance is another draw for young people. Regimented caffeine can boost endurance and short-term athletic performance, Roberts said -- but it can also make athletes too jittery.

In a letter to athletes on behalf of the Minnesota State High School League, Roberts wrote: "Energy drinks seem to reduce performance for technical skills that rely on timing and coordination; not attributes that help most athletes."

While Virginia banned energy drinks at high school sports, the Minnesota league stopped short of such action. "It's hard to ban something unless you're really willing to step in" and force violators to miss games, Roberts said.

Jeannie Crandall said the pressure is so great among athletes in Hill City, Minn., that some took caffeine supplements until parents and coaches intervened. "These girls were finding that the crash was really, really bad," she said.

Her 16-year-old tried 5 Hour Energy before a basketball game, but felt worse. Now she drinks them only to try to stay up all night at sleepovers.

Health officials are concerned enough that the nation's poison control centers are now tracking caffeine overdoses related to energy drinks. In 2011, the centers have reported 331 incidents. More than half involved children and teens. One in five involved elevated heart rates. Forty-six had major or moderate effects.

Singh agreed that any source of excess caffeine can cause hypertension and other problems for children. But she still thinks energy drink companies deserve scrutiny due to their youth marketing.

"We really don't want our teenagers drinking tons of coffee per day," she said, "but to me the issue is that [energy drink makers] are targeting youth and making these unscientific claims about the other ingredients that they throw in."

Jeremy Olson • 612-673-7744 Taryn Wobbema, a University of Minnesota journalism student on assignment for the Star Tribune, provided reporting for this story.