Teenagers who drink more than five cans of soft drinks a week are significantly more likely to get into fights or carry a weapon, new research suggests.

The study looked at 1,878 teens from Boston, who were asked how many non-diet soft drinks they had consumed over the past week. The teens largely represented ethnic minorities from low-income neighbourhoods.

The researchers then asked the teens if they had been violent toward their peers, siblings, or a partner, and if they had carried a gun or knife over the past year.

Those who drank five or more cans of soft drinks a week were significantly more likely to have consumed alcohol and smoked at least once in the previous month. But even after controlling for these and other factors, those who drank five or more cans of pop a week were more likely to exhibit aggressive behaviour.

And the more pop they drank, the higher the chances they had of being violent or aggressive.

Just over 23 per cent of those drinking one or no cans of soft drink a week carried a gun or knife, rising to just under 43 per cent among those drinking 14 or more cans.

The proportions of those being violent toward a partner rose from 15 per cent in those drinking one or no cans a week to just short of 27 per cent among those drinking 14 cans or more.

Similarly, violence toward peers rose from 35 per cent to more than 58 per cent, while violence toward siblings rose from 25.4 per cent to over 43 per cent.

The study's findings appear in the journal Injury Prevention.

One of the study's authors, Prof. Sara Solnick of the department of economics at the University of Vermont, says even her team was surprised by their findings.

"We thought that when we controlled for cigarettes and tobacco, the effect would disappear," she says. But instead, soft drink consumption was still what mattered.

"Even if kids used tobacco or alcohol, or they did not, it still boosted the risk," she said.

She says the fact that the aggressive behaviour rose with the amount of pop was intriguing.

"When you see a behaviour increase as the dose increases, that is very suggestive there is something happening there," she said.

The authors say there could be a cause-and-effect relationship, perhaps due to the sugar or caffeine content of soft drinks. Or, they say, there could be other factors. Perhaps, those who drink a lot of soft drinks don't have otherwise healthy diets and the pop drinking could simply be a reflection of that.

"We can't explain why this is happening," Solnick said. "What we have now is just an association. People who are involved in a lot of aggression also drink more soda and we don't know why."

Study co-author David Hemenway of the Harvard School of Public Health says more research is needed.

"We need lots more studies to look at people who are not just in Boston, who aren't just teenagers, and so on, to see if we can get a better understanding of why this relationship is so strong," he told CTV's Canada AM.

Registered dietician Rosie Schwartz wonders whether it's the sudden surge of sugar that could trigger bad behaviour.

"When kids or adolescents have sugar or pop on its own, it can lead to a quick rise in blood sugar and a quick drop and that can lead to more stress hormones, and that can lead to aggression," she suggested.

Her message to parents is to limit the intake of pop, especialy in already aggressive kids.

The Canadian Beverage Association, meanwhile, declined to comment to CTV News on the study.

With a report from CTV's Avis Favaro and producer Elizabeth St. Philip