"It's really hard to explain the link," Dr. Elias Aboujaoude, a Stanford University researcher who was not involved in the study, told Reuters Health.
"It often becomes a chicken and egg issue: are they online because they're depressed or are they depressed because they're spending inordinate amounts of time online?" explained Aboujaoude, the author of the book Virtually You: The Dangerous Powers of the E-Personality.
The answer to that question, in turn, is critical for whether or not exaggerated Internet use should be considered a problem in its own right.
Led by Yale University's Dr. Timothy Liu, the authors of the new study surveyed students at ten different high schools in Connecticut, asking more than 150 questions about health, risky behaviors, and impulsiveness -- including seven questions on Internet use.
Specifically, Liu and his colleagues used three questions to determine if a student had "problematic Internet use." They asked students if they had ever had an "irresistible urge" to be online, if they had experienced "a growing tension or anxiety that can be relieved only by using the Internet," or if they had tried to quit or cut down on using the Internet.
Out of 3,560 students, four percent met the criteria for problematic Internet use. Asian and Hispanic students were most likely to qualify as problematic users -- although the majority of students in the study, published in The Journal of Clinical Psychiatry, were white.
Girls were more likely to answer yes to one of questions on problematic Internet use, but more boys said they spent in excess of 20 hours a week online -- about 17 percent of boys, compared to 13 percent of girls.
Students who were problematic Internet users according to the survey also tended to be more depressed and would get into serious fights more often. And boys in that category had higher rates of smoking and drug use.However, they didn't do any worse in school based on their grades.
Liu and colleagues note that the findings can't prove a cause-and-effect relationship between problematic Internet use and depression and drug use.
They say that more research is needed to get at the causes behind different kinds of Internet use -- such as social networking and role-playing games.Preliminary evidence, Aboujaoude said, suggests that problematic Internet use shares common features of drug and alcohol abuse disorders, obsessive-compulsive disorders, and disorders where people have trouble controlling their pleasure-seeking impulses.
Dr. Jerald Block, a psychiatrist at Oregon Health & Science University, said that to him the evidence points toward an addiction."There seems to be common pathways within the brain for addictive behaviors, of which pathological gambling is one example," he told Reuters Health. "I would say that there's sufficient data to show that pathological computer use is another example of an addictive behavior."He also suggested that because rates of computer use were based on students' responses about their own behavior, the new study might be underestimating the number of kids who actually have the problem.
There's not a one-size-fits-all way to treat problematic Internet use, said Liu, the new study's author.
"I would support treating all the underlying conditions (such as depression) as you would treat anyone with psychiatric illness," he told Reuters Health. But, he added, "we don't really have a lot of evidence for treatment."
Block said that while it might take some time, he has "absolutely no doubt" that psychiatrists will eventually recognize problematic Internet use as its own disorder."When you start using (the computer) 30 hours a week, it becomes a container for emotion," he said. "It occupies time. The computer itself becomes a significant other, becomes a relationship."