From Correspondent Linda Ciampa

ATLANTA (CNN) -- Researchers at Harvard University have found that, for most, gambling starts during the teen years and is often linked to other risky behavior.

A survey of 17,000 eighth- through 12th-grade students in Vermont found that 53 percent of them said they gambled in the last 12 months, and 7 percent said the practice caused problems with friends and family, according to a report published in the journal Pediatrics.

Between 76 percent and 91 percent of all teen-agers will have gambled by the time they reach their final year of high school, estimate researchers at Harvard Medical School's Children's Hospital in Boston.

It may be the Super Bowl, the Final Four or the Stanley Cup finals, and it may seem like fun, as some claim, but the researchers found that there is a strong link between gambling and using illegal drugs or alcohol, having unprotected sex and carrying weapons.

"What we found was that youth who had gambled were more likely to have engaged in those risk behaviors," says Dr. Elizabeth Goodman of Children's Hospital. "And youth who had problems related to gambling were more likely to have engaged in more."

Fifteen percent of those in the study who had gambled in the past year also had used illegal drugs, double the rate of those who had not gambled.

Among those who reported that gambling caused them problems, the proportion also using illegal drugs rose to 28 percent.

More chances to get hooked early

The researchers also discovered that gambling teen-agers were approximately twice as likely as non-gamblers to have been in a fight or to have carried a weapon in the last month.

Dr. Michael Gordon of the Ridgeview Institute in suburban Atlanta treats pathological gamblers -- a group that experts say comprises about 4 percent of the U.S. population.

Gordon says that with the growth of casinos, lotteries and the Internet, there are more opportunities than ever to get hooked early.

"This starts in adolescence about 95 percent of the time," Gordon says. "So you're having young people getting themselves into serious difficulties rather than establishing a foundation for their future."

One such example is "Terry," who remembers betting as early as 11, and who says the compulsion to gamble can easily lead to trouble.

"When you run out of money, as you run out of alcohol or drugs, you find ways to get it," he says. "And that usually leads to breaking the law ... to stealing."

Early intervention needed

"Terry" gambled into adulthood, and isn't sure which came first, but he knows gambling influenced his problems with drugs and alcohol. He began to turn his life around when he entered a treatment program nearly five years ago.

"It's neat to be able to go to a football game knowing I don't have any (bets)," he says. "It doesn't matter if the guy fumbles or trips or goes over the goal line."

The research at Harvard doesn't prove gambling actually causes kids to drink or smoke, but the researchers say the odds are high that gambling will tempt teens to try other dangerous behavior.

They also say the study highlights the need for early intervention programs.