A study has found that teenagers are more likely to be aggressive and violent if they consume more than five cans of soda a week.

The research published online in the journal Injury Prevention suggests that teenagers with a high consumption of carbonated, non-diet soft drinks are more likely to engage in violent and aggressive behaviors. Researchers analyzed the data based on sex, age, race, body mass index, sleep patterns, tobacco use, alcohol use, and having family dinners. They found that heavy soft drink consumption had the same effect as tobacco and alcohol on violent tendencies.

"This is just one study, and it needs to be looked at in more detail." said Dr. David Hemenway, professor of public health and director of the Injury Control Center at the Harvard School of Public Health and the study's lead author in an interview with Medscape Medical News.

Although Hemenway was reluctant to say if the link between soft drink intake and violence is causal, he didn't completely rule it out. There are other factors that need to be studied including caffeine content in the soft drinks.

The study used data from the Boston Youth survey which asked participants how many non-diet fizzy drinks they had a week. Intake of up to four cans was considered "low" and five or more "high". The researchers then looked at links between soft drinks intake and violent behavior.

Hemenway and his team found that teenagers who drank more than five 12-ounce cans of carbonated soft drinks were more likely to participate in violent and aggressive behavior. Of those adolescents who drank more than 14 or more cans per week, 42.7 percent carried a gun or knife, 58.6 percent were violent toward their peers, 26.9 percent were violent toward dates, and 45.3 percent perpetrated violence toward other children in their family. These results were significantly higher than those who only drank five or less cans a week.

Not everyone in the medical community is convinced about the study's results. Dr. Marion Nestle, professor of nutrition, food policies and public health at New York University School of Medicine, was not impressed with the study design.

"This looks like a 'tracking' study to me. I don't see how the study can conclude anything specific about soft drinks except guilt by association," she said in an e-mail to Medscape Medical News. She added that "poor kids drink more soft drinks than rich kids, and they are marketed to more aggressively.

"If it turns out that alcohol and junk food diets can be linked to negative behaviours," she said, "soda companies will reap what they sowed when they focused so much marketing on low-income, minority communities."