"The results clearly show that there is a strong correlation between media exposure and long-term negative health effects to children," said Ezekiel Emanuel of the National Institutes of Health, lead researcher on the study.
The study, "Media and Child and Adolescent Health: A Systematic Review," was done by the Yale University School of Medicine, National Institutes of Health, and California Pacific Medical Center and published by Common Sense Media.
It looked at the best studies on media and health from the last 28 years, a total of 173 in all, and found that 80 percent of them showed that greater media exposure led to negative health effects in children and adolescents.
The study examined media exposure and seven health outcomes: tobacco use, early sexual behavior, childhood obesity, attention deficit disorder with hyperactivity, low academic performance, drug use and alcohol use.
"This review is the first ever comprehensive evaluation of the many ways that media impacts children's physical health," said Emanuel, whose brother, Rahm Emanuel, is chief of staff to president-elect Barack Obama.
The strongest link was found between media and obesity with 86 percent of 73 studies finding a strong relationship between increased screen time and obesity.
Eight-eight percent of 24 studies examining media and tobacco use found a statistically significant relationship between increased media exposure and an increase in smoking at an early age.
Of eight studies on media and drug use, 75 percent found a statistically significant relationship between media exposure and drug use while 80 percent of 10 studies reported a statistically significant association between media exposure and early alcohol use.
Sixty-five percent of 31 studies evaluated reported a statistically significant association between increased media exposure and poor academic outcomes such as low standardized test scores or grades.
Sixty-two percent of 26 studies which analyzed the number of hours spent watching television reported a significant relationship between greater media exposure and low academic achievement.
On a positive note, one study of Internet use did find that increased access to certain types of websites was associated with better school performance.
Thirteen of 14 studies (93 percent) found a statistically significant association between media exposure and early sexual behavior.
As for attention deficit disorder with hyperactivity, nine of 13 studies (69 percent) found an association between media exposure and increased attention problems.
According to the study, the average child or adolescent spends nearly 45 hours per week with media, compared with 17 hours with parents and 30 hours in school.
The study's authors said most of the quality studies available focused on television, movies and music and said future research should look at the impact of the Internet, video games and cellphones.
"This study provides an important jumping-off point for future research that should explore both the effects of traditional media content and that of digital media such as video games, the Internet, and cellphones which kids are using today with more frequency," said Emanuel.
The authors of the study recommended that parents place limits on the amount of media their children consume, ensure they watch age-appropriate programs and encourage them to spend more time playing outside.
"Parents and educators must consider the effects of media when they're trying to address issues with their child's health," said James Steyer, chief executive and founder of Common Sense Media.