LANSING – A new study by University of Michigan researchers found that two-thirds of parents believe their teens drink a caffeinated beverage at least one day per week, with a quarter reporting their teens drinking caffeine most days.

Heavy caffeine consumption can cause serious health problems, but some beverages popular with teens can hide large caffeine amounts. Researchers think parents may not be aware of just how much caffeine their teens are consuming.

Sarah Clark, the co-director of the C.S. Mott Children’s Hospital National Poll on Children’s Health, said she got the idea for the survey by listening to parents.

“I’m a big eavesdropper,” she said. “I might be at the grocery store or the airport or the park. I’m listening to what parents are talking with their kids about, what parents are talking with each other about.”

Clark said she noticed that teens were meeting up with friends at coffee shops. She did not remember that being common when her sons were that age 10 to 15 years ago.

Another thing that caught her attention was Panera Bread’s “charged lemonade” controversy that prompted lawsuits claiming the drinks’ high amounts of caffeine caused health problems and even two deaths in Florida and Pennsylvania.

“I remember somebody making a comment of ‘why wouldn’t people know that it had so much caffeine,'” she said. “I remember thinking, ‘Why would you know that? Who walks around knowing what a caffeine limit is?'”

So she conducted a national online poll on parents’ perceptions of caffeine use by their teenage children for the monthly Mott Poll.

The results appear in the journal Preventive Medicine Reports.

What the researchers found was reason for concern, experts say.

Nearly 10% of the parents reported daily use of caffeine by their teens.

They also found that most parents who reported daily caffeine consumption rarely looked at caffeine amounts.

About a third said their teen had not heard about the risks of too much caffeine from parents, another relative, school staff or health care providers.

Most parents thought their teen drinks caffeine mainly because of the taste of the beverage, because their favorite products contain it or their friends drink it.

“So it isn’t like all the kids are seeking caffeine to stay awake,” Clark said. “I felt like that was important.”

Part of the confusion is the lack of clear guidelines in the U.S. about safe amounts of caffeine for teenagers.

The Food and Drug Administration recommends that adults drink no more than 400 mg of caffeine per day – that’s equivalent to about two cups of coffee.

The FDA provides no recommendations specifically for teenagers, though it advises children and teens to avoid energy drinks because of caffeine, added sugars and other additives.

The American Academy of Child and Adolescent Psychiatry recommends limiting teenagers’ caffeine use to 100 mg or less – the amount in about two sodas.

But caffeine amounts vary widely in beverages.

“There are sports drinks that have caffeine. If you go to some chain restaurants, you think you’re ordering a lemonade, but it may actually have sometimes 200 to 400 mg of caffeine in it,” said Amy Reed, a registered dietician nutritionist and representative of the Academy of Nutrition and Dietetics.

“It’s kind of gotten out of hand,” she said.

In January a collaboration of health and nutrition organizations released guidelines for kids and teens. They recommend 5- to 18-year-olds avoid beverages with caffeine or other stimulants, along with sugar-sweetened beverages and those with non-sugar sweeteners.

The report recommended drinking plain water, plain pasteurized milk and limited amounts of 100% fruit and vegetable juice.

The research was a collaboration among the Academy of Nutrition and Dietetics, American Academy of Pediatric Dentistry, American Academy of Pediatrics and the American Heart Association and was led by the nonprofit organization Healthy Eating Research.

Reed said parents should talk to their kids about the extra caffeine in beverages.

Caffeine is a diuretic and can contribute to dehydration, she said.

“If your child is going to an all-day soccer tournament, we know it’s important to replace electrolytes,” Reed said. “But make sure you’re not purchasing those sports drinks that have caffeine in them.”

The dangers of too much caffeine go beyond dehydration, however.

“The American Academy of Pediatrics has warnings about drinking energy drinks that have a lot of added caffeine,” said Tamara Hannon, a professor of pediatrics at Indiana University and a former member of the American Academy of Pediatrics’ Committee on Nutrition.

“Parents should just be aware that caffeine is not a benign substance, even though it’s in a lot of things and it is naturally occurring,” she said.

Hannon said small doses can help with focus and attention, but consuming more than your body can handle can lead to unwanted side effects such as hyperactivity, inattention, nausea, lack of appetite and headache.

Too much caffeine can also disrupt sleep, Hannon said.

“Teenagers already don’t get enough sleep, so that can be very problematic,” she said.

Clark, the co-author of the Mott Poll, said she thinks parents probably underestimate the amounts of caffeine their child is consuming.

“It’s not even kids being sneaky,” Clark said. As teenagers spend more time away from home, it’s difficult for parents to keep track.

“There are so many coffee products and there are so many enhancements,” Clark said. “It makes it harder for people to understand their own consumption, and harder for parents to understand their child’s consumption.