The gamer community had a near-miss this week in Ohio, when a 15-year-old boy collapsed after playing "Call of Duty: Modern Warfare 3" for up to five days straight.

The Columbus teen was rushed to the hospital with severe dehydration, where he recovered, according to a report from TV station WCMH on Aug. 7.

Players who delve too deeply into their electronic worlds can face various health risks, ranging from deep vein thrombosis, or blood clots, to severe dehydration.

For instance, in July, a Taiwanese teenager was found dead after sitting for 40 hours in an Internet cafe playing "Diablo 3." At the time, doctors speculated he died from a heart attack caused by a blood clot that formed during the long session.

And last summer, a 20-year-old man from the U.K. died from a blood clot after spending 12-hour sessions on his Xbox. His father told "The Sun" newspaper, "He lived for his Xbox. I never dreamed he was in any danger." [10 Easy Paths to Self Destruction]

While these are extreme cases, they are a reminder that sitting at a computer or console for days, whether it's for "World of Warcraft" or for work, isn't healthy for anyone. But psychologists who study video games and kids say parents needn't worry about the amount of time spent gaming, unless screen time starts to affect school, health or social life. (And, of course, a stint of tens of hours gaming is likely to negatively affect schoolwork and lead to social woes.) That said, researchers remain concerned about the effects of violent content in video games, which have been linked by many studies to aggressive behavior.

Too much screen time?

These days, screens of one kind or another occupy youth for 50 hours a week, a 2010 survey by the Kaiser Family Foundation reports. "It's a full-time job plus 10 hours of overtime, and that's the average," said Douglas Gentile, a psychologist and director of the Media Research Lab at Iowa State University.

Video-gaming consumed nine weekly hours for teens, the Kaiser survey found, while a Harris Poll conducted for Gentile during the same period reported 13 hours a week spent gaming on computers and consoles.

While some kids can shoot 'em up for hours, for others, too much time gaming leads to poor school performance. Recent studies have finally linked the cause and effect, showing that gaming displaces after-school academic activities such as homework and reading. A 2010 study from researchers at Denison University in Ohio, published in the journal Psychological Science, compared two groups of boys that had never owned gaming systems. They gave one group a system right away, but withheld games from the other group for four months. Boys who received the video-game system first had more teacher-reported learning problems and significantly lower reading and writing scores than the other boys.

Problems in school are relatively easy for parents to fix: Limit screen time — of course, if you can get the controller out of his or her hands. The American Academy of Pediatrics recommends no more than one to two hours per day in front of any electronics.

Violent games and aggression

What's harder to control is violent content in video games. The Pew Research Center reported in 2008 that more than 90 percent of games rated as appropriate for children 10 years or older contained violence, including games rated "E" for everyone. (Most researchers define violence as the ability of a player to intentionally harm others in a game.)

Now most researchers will agree that video games can help as well as harm. For example, educational games boost learning, and action games can improve vision and spatial skills. Video games have also been used successfully to teach children self-care skills for asthma and diabetes.

And then there's the primary reason people play video games: They're relaxing. Gentile thinks the flickering screen and varying sound levels trigger a primitive brain response. "One of the reasons I think we find television and video games so relaxing is they provide the attention for you. It forces you to orient to the media. You don't have to work to pay attention like you do in [a] classroom lecture," said Gentile.

But a preponderance of evidence links violent video games to an increase in aggressive behavior in teens. The behavior wasn't violent crime, like school shootings, but small yet hurtful offenses like teasing, name-calling, rumor-spreading and fist fights. In a review of 130 studies of kids and teens, Iowa State University researchers found that violent video games increased the likelihood of aggression and decreased empathy. The meta-analysis appeared in 2010 in the journal Psychological Bulletin. [5 Ways to Foster Self-Compassion in Your Teen]

Which teens are vulnerable?

Of course, repeated exposure to violence in any environment has a deleterious effect, Gentile noted. "Seeing violence anywhere increases the risks that a child might become involved in aggression, whether as a perpetrator or a victim," he said. But video games are phenomenal teachers. Players get immediate feedback and rewards for punishing competitors. And not only do games reward hostility, they train your brain to respond to real-life problems with aggression, research indicates.

In fact, games can prime teens to react to slights with name-calling or pushing, instead of choosing to avoid confrontation. "So when I get bumped in the hallway, I don't assume it's an accident anymore," explained Gentile. "What comes to mind first is to retaliate in some way. Those aren't the only options you have, but we never think of them because what we see over and over in the media is 'You killed my monster, now you must die.'"

But psychologist Patrick Markey's research suggests just some teens are susceptible to these effects. Markey found people withcertain personality traits — those who are highly neurotic, less agreeable and less conscientious — are those more likely to become hostile from gaming. The 2010 study appeared in the journal Review of General Psychology.

"The truth of the matter is that most people can handle this media, but for some people with a select predisposition, these people might be a little more aggressive, more prone to an argument here and there," said Markey, a professor at Villanova University in Pennsylvania.

"The most interesting part is there is really no research that suggests video games have a different effect than TV or movies. It has empirically never been shown," said Markey. "Any media is supposed to engage us emotionally, and video games are a form of media, a form of art even."