U.S. National Institutes of Health, Yale University and the California Pacific Medical Center experts analysed 173 studies done since 1980 in one of the most comprehensive assessments to date on how exposure to media sources impacts the physical health of children and adolescents.
The studies, most conducted in the United States, largely focused on television, but some looked at video games, films, music, and computer and Internet use. Three quarters of them found that increased media viewing was associated with negative health outcomes.
The studies offered strong evidence that children who get more media exposure are more likely to become obese, start smoking and begin earlier sexual activity than those who spend less time in front of a screen, the researchers said.
Studies also indicated more media exposure also was linked to drug and alcohol use and poorer school performance, while the evidence was less clear about an association with attention deficit hyperactivity disorder, they added.
"I think we were pretty surprised by how overwhelming the number of studies was that showed this negative health impact," NIH bioethicist Dr. Ezekiel Emanuel, one of the researchers in the report released by the advocacy group Common Sense Media, said in a telephone interview.
"The fact that it was probably more a matter of quantity than actual content is also a concern. We have a media-saturated life right now in the 21st century. And reducing the number of hours of exposure is going to be a big issue."
Experts for decades have worried about the impact on young viewers of the violence and sexual content in some TV programs, movies and video games. Another issue is that kids are spending time sitting on a couch watching TV or playing computer games when they could be running around outside.
One study cited in the report found that children who spent more than eight hours watching TV per week at age 3 were more likely to be obese at 7. And research shows that many U.S. children, even toddlers, watch far more.
Dr. Cary Gross of Yale University School of Medicine in New Haven, Connecticut, another of the researchers, said TV and other media content can have a profound impact on children's attitudes and beliefs, most notably among teens.
He cited a U.S. study by the RAND research organisation published in November that showed that adolescents who watched more programing with sexual themes had a higher risk of becoming pregnant or causing a pregnancy.
Thirteen of 14 studies that evaluated sexual behavior found an association between media exposure and earlier initiation of sexual behavior, the researchers said.
Do you try to limit your child's media consumption? Which media source is your child's biggest vice - TV, Internet, electronic games or other sources?