A new study suggests that the high school students who spend the most time texting or on social network sites (or both) are at risk for a host of worrisome behaviors, including smoking, depression, eating disorders, drug and alcohol abuse, and absenteeism.

The study by researchers at Case Western Reserve University, presented Tuesday at a meeting of the American Public Health Association in Denver, is based on data from questions posed last year to more than 4,000 students at 20 urban high schools in Ohio. About one-fifth sent at least 120 text messages a day, one-tenth were on social networks for three hours or more, and 4 percent did both.

That 4 percent were at twice the risk of nonusers for fighting, smoking, binge drinking, becoming cyber victims, thinking about suicide, missing school and dozing off in class.

The researchers emphasized that texting and social networking did not necessarily cause the other problems. But the lead author, Dr. Scott Frank, a family physician who is director of the public-health master’s program at Case Western Reserve School of Medicine, said:

“It does make sense that these technologies make it easier for kids to fall into a trap of working too hard to fit in. If they’re working that hard to fit in through their social networks, they’re also trying to fit in through other behaviors they perceive as popular, like smoking cigarettes or drinking alcohol, having sex and getting involved in higher-risk adolescent behaviors.”

Girls, members of minorities, and teenagers from low-income backgrounds or female-headed households were at greater risk, but the pattern persisted even after researchers controlled for those factors. (One in five teenagers reported no texting and no online social networking at all.)

Dr. Frank noted that the most avid texters and social networkers also rated their parents as more permissive. “This is a red flag for parents — a red flag for their parenting,” he said, “because they need to be monitoring and taking charge of the choices their kids are making. We want parents to set more restrictive rules for their kids regarding texting and networking, just as they would set rules about whether their child can go out on a school night and socialize for three hours.”