Close to one in 10 U.S. children and teenagers who play video games are addicted and suffer problems in their school and family lives as a result, a research firm said Monday.

A January survey of more than 1,100 youths from ages 8 to 18 found that addicted gamers receive lower grades in school than their peers and are more likely to have been diagnosed with an attention deficit problem, Harris Interactive said.

Researchers involved in the study said the prevalence of gaming among young people made the findings a reason for concern. "Almost one out of every 10 youth gamers show enough symptoms of damage to their school, family, and psychological functioning to merit serious concern," Douglas Gentile, director of the Media Research Lab at Iowa State University, said in a statement.

Video game addicts are more likely to have game consoles in their bedroom and spend an average of 24.5 hours per week shooting imaginary bad guys in the virtual worlds. Besides being more likely to perform poorly in school, addicts get into more physical fights and are physically heavier than nonaddicts.

Other findings are that nearly a quarter of the respondents in the online survey said they feel addicted to video games. Fully 44% of the youth said their friends are addicted. Nearly eight in 10 U.S. children and teenagers play video games at least once a month.

The amount of time played differs by age and gender. Harris found the average 8- to 12-year-old plays 13 hours of video games peer week, while the average 13- to 18-year-old plays 14 hours per week. Boys in general played almost twice as much as girls.

While people over 18 were not covered in the study, a report released last year by the Entertainment Software Association found that video and computer games were as attractive to adults as to teens. Fully 44% of gamers were between the ages of 18 and 49, and 31% were under 18 years old. Males accounted for more than three out of every five players.

Not all research on video game play is negative. A study conducted last year by Beth Israel Medical Center in New York found that surgeons who played video games before participating in a performance test completed it more than 11 seconds faster than those doctors who didn't play the games.