The U.S. National Institutes of Health, Yale University and the California Pacific Medical Center reviewed a number of 173 researches that study the impact of mass-media on children’s development and the potential damage they can inflict, resulting in the most elaborate meta-analysis ever to be done on this matter.

The conclusions were clear: there is a strong correlation between the average time of exposure to media content and health problems. Among them, the most important are drug, alcohol and tobacco use, childhood obesity, low academic achievement and increased prevalence of ADHD. Also, exposure to erotic content influences the age of starting sexual activity.

In general, a modern child spends about 45 hours a week with TV, whereas he spends 30 hours at school and just 17 hours with his parents. “The average parent doesn’t understand that if you plop your kids down in front of the TV or the computer for five hours a day, it can change their brain development, it can make them fat, and it can lead them to get involved in risky sexual activity at a young age,” said Jim Steyer, the chief executive of Common Sense Media.

A main issue is that, among these studies, only a small part of them show the influence of the main modern types of media content: “Media has evolved at a dizzying pace, but there’s almost no research about Facebook, MySpace, cellphones, et cetera,” Mr. Steyer said.

Even though there are positive studies that find a series of advantages for the use of the Internet among teenagers, there is still a big concern about what the overall effect of the media is in our children’s education.