New research published in the medical journal Injury Prevention suggests a link between high soft drink consumption in teens and aggressive behaviour.

The study, which analysed the soft drink consumption of 1,878 Boston public school students, showed teens who drank more than five cans of non-diet soft drink a week were 9 to 15 per cent more likely to act aggressively than those who consumed less.

The authors surveyed the teens, who came from largely African American and Hispanic backgrounds, asking them how much fizzy soft drink they consumed as well as whether they carried a weapon or showed violence towards those around them.

"Heavy use of carbonated non-diet soft drinks was significantly associated with carrying a gun or knife and violence towards peers, family members and partners," authors David Hemenway and Sara Solnick said in a statement.

While cautioning against making too many judgments based on the results, researchers found the increase in aggressive behaviour remained despite taking into account factors including age and gender, alcohol and cigarette consumption and average amount of sleep.

"Consumption of high quantities of soft drinks resulted in a 9 to 15 per cent point increase in the probability of engaging in aggressive actions," the study said.

"The impact of high soft drink consumption on violence was similar in magnitude to the impact of using tobacco or using alcohol, but the influence of soft drink consumption on the probability of carrying a weapon, while significant, was not as strong as the influence of alcohol or tobacco consumption."

The research also found evidence of a dose-response relationship, where the likelihood of violence towards others increased alongside soft drink consumption beyond five cans per week.

Based on the findings, while they could not rule out other unaccounted factors, the authors said "there may be a direct cause-and-effect relationship, perhaps due to the sugar or caffeine content of soft drinks".

They also said soft drink consumption could be a useful tool for analysis and prediction of violent behaviour.

"Even if soft drinks are only a marker for violence rather than on the causal pathway, they may be a highly useful marker since, at least in our study, the association between soft drink consumption and violence is not only significant but also strong and addictive to that of both alcohol and tobacco use," they said.

More work needed

While Australian experts say the results are interesting, they have cautioned against reading too much into the findings.

Professor Mike Daube, director of the Public Health Advocacy Institute, said at this stage the only definite conclusion to be drawn from the study was the link between poor diet and economic disadvantage.

"A lot of young people do drink soft drinks, and young people that are disadvantaged and more likely to be involved in violence, probably also have a poorer diet," he said.

"So I think it's a marker, it's primarily telling us that people who are more likely to be violent come from backgrounds where their overall diet isn't very good."

But he said there was no doubt that diet could affect behaviour and further research could be valuable.

"There are some aspects of diet that we know contribute substantially, for example alcohol, which has a huge impact on violence; we also know broadly put diet is harmful in terms of overall development," he said.

"So yes there is absolutely a need for more research in relation to diet and disadvantage and various forms of behaviours, but my caution is against taking too much from this.

"What we can say is it gives us interesting results, but I don't think that we can instantly assume from this that one can of Coke is going to lead to dramatic increases in assaults."

Teenage aggression

Dr Karena Burke, senior lecturer in psychology at Central Queensland University, while also ruling out a definite causal link, said the research had implications for Australia in light of the rise in soft drink and energy drink consumption.

"It's one of the rare studies that actually looks at teenage aggression and at some sort of association with their diet. There's not a lot of that sort of research that's out there," she said.

Dr Burke also said not enough was known about the effects of soft drink on behaviour, with the current generation of teenagers exposed to a level not seen before.

"I think if you looked at the trends over time, adolescents today would be drinking a lot more of these drinks than a group of adolescents say 15 or 20 years ago," she said.

"So we don't know what the long-term effects are because in effect this is probably the first generation where we've had that availability so readily, where we're going to see consumption across such a long period.

"But I guess it really comes back to that whole 'you are what you eat'; if we move back to diets that are less processed and rely less on packaged foods, we may see a decrease in both physical and psychological health problems."

Misperceptions

The Australian Beverages Council has hit back at the research, with chief executive Geoff Parker saying it may result in misperceptions about soft drinks.

"The authors of this study have failed to factor out other important considerations and did not prove cause and effect," he said in a statement.

"The fact remains that there is no scientific evidence to support that young adults who consume sugar-sweetened beverages are more likely to engage in violence.

"The conclusions of the authors, who surveyed less than 1,900 Boston public high school students, are not representative of the broader US teen population. Unfortunately this study may result in false misperceptions about sugar-sweetened beverage consumption with no scientific evidence.

"The authors themselves note that they do not know the reason for the association between soft drinks and the perpetration of violence."