The coffee culture has become a teenage concept. One Starbucks coffee shop in New York City is standing room only for the under-18 set on weekend nights, and both the beverage and the hangout seem to have parents' blessings.

But what about caffeine - that "drug" - and its effect on growing bodies? "We had the whole discussion with my bio teacher about this," said Michelle Gort, 15, and a Starbucks habitue, "and she was like, no, it doesn't do anything."Coffee consumption is up among 10- to 19-year-olds across the country, according to a recent study, leav-ing its mark on the adolescent lexicon. Teenage boys from one Manhattan high school refer to one group of young females as "the latte girls," stereotyping them by a choice of coffee - a little espresso and lots of milk - that would not have been widely understood five years ago. References to "java junkies," who drink coffee to excess, to become "jazzed on java," crop up in movies and on television.

Coffee containers appear regularly in high school classrooms with the teachers' permission. Thanks to a lingering association with adult sophistication, a cup of coffee has gained the kind of cachet that cigarettes enjoyed years ago.

It is both stimulant and social vehicle. "My friends stay up late and use coffee sometimes to wake themselves up," said Sarah Church, a 15-year-old who attends Berkeley High School in Berkeley, Calif., where espresso and iced coffee are in. "We're sophomores, and we have the most homework of anybody."

According to the National Coffee Association, whose annual Winter Coffee Drinking Study tracks how many cups are drunk by various demographic groups, 5 percent of the 10- to 19-year-olds surveyed said they drank some kind of coffee in 1988. In 1997, 8 percent drank coffee.

Over that same 10-year period, the percentage of youths drinking decaffeinated coffee fell to 0 from a mere 2 percent. That may be a statistical blip, said Robert Nelson, president of the coffee association. Or it may reflect the sentiments of a generation raised without fear of caffeine.

Concerns still center on caffeine's effect on calcium absorption, but studies so far have been inconclusive. Caffeine is a drug, says Don Hensrud, an assistant professor of preventive medicine and nutrition at the Mayo Clinic.

"The data aren't all that strong in terms of severe disease and caffeine," he said, "but what I find is there are many more subtle effects that can affect people quite a bit, including insomnia, morning headaches and weekend headaches, gastrointestinal side effects like constipation or diarrhea."

"There can be calcium loss in the urine, which is significant for young people who are trying to establish good peak bone mass early in life, before they begin to lose bone," Hensrud added.

The Starbucks coffee chain, a ubiquitous purveyor of coffee to the young and restless, says it is not trying to attract teenagers. "As a company, we don't market to teens," said Cheri Libby, a spokeswoman for the chain. "We have a lot of different types of profiles of people who drink coffee. But we don't even track that segment."

Caffeine is already a dietary staple for many American children, who start drinking colas and other caffeinated sodas as toddlers.

"I have seen a lot of females who drink a lot of caffeinated beverages during the day at the expense of eating," said Heidi Schauster, a clinical dietitian specialist who works with anorexic and bulimic children at Children's Hospital in Boston. "Most of the time it's diet soda, but more kids are drinking coffee."

But even she isn't too worried about coffee. "It's one of those vices that we can still have," she said. "I'd certainly rather have my kids start drinking coffee than picking up a cigarette."