The latest studies have shown that teenagers are becoming a larger percentage of the coffee drinkers and the statistics are causing concern among doctors and they say parents should be concerned too.

Sixteen-year-old Jessica Shipley starts every morning with a cup of coffee.

"Some days when I'm, like, really tired, having coffee, like, does the trick," said Shipley.

Seventeen-year-old Maya Agger has been drinking coffee since she was 6-years-old.

"Caffeine doesn't do anything for me anymore," said Agger.

The fact young teens are getting through their day on caffeine is surprising to some.

"It shocks me a little bit," said Jessica Dowell, coffee shop employee. "I don't think I could function in school drinking that much caffeine, it would knock me out."

Studies have shown that 25 percent of teens reports daily coffee consumption and market research indicates that the number of coffee drinkers increases an average of 12-15 percent every year.

"I think there is good cause for concern," said Nanette Steinle, M.D., University of Maryland School of Medicine. "Mostly in mental and physical development, establishing and maintaining a good sleep cycle."

Doctors say that too much caffeine causes headaches, fatigue and irritability, plus memory, learning and mood problems. It is also more potent in teens' smaller, growing bodies.

Coffee drinks are full of fat and sugar, which puts teens at risk for obesity and cardiovascular disease later in life.

"They'll come in and get a coffee with three shots of espresso and then some sugar syrup in it and then ass more sugar to it," said Dowell. "It's just crazy."

Doctors also say that parents should limit children's consumption to one cup or about 400-milligrams of total caffeine each day.

Some kids have decided to limit their intake themselves.

"I need it not in the mornings," said Lianna Kissinger, teen coffee drinker. "I'm trying to cut back because that's a stupid way to live."

Doctors say they hope that kind of thinking among teens catches in and while too much caffeine can be bad for teens, a small amount can actually make them more alert. It can also improve physical and mental performance.