Teenagers are significantly more likely to be aggressive and violent if they regularly consume fizzy soft drinks, according to a new study.
It claimed consumption of more than five cans of non-diet carbonated drinks a week was associated with behaviour that included carrying weapons and violent assaults.
The US researchers do not yet know if the link is causal, but have not ruled this out. It may be that unknown factors causing aggression in youngsters also influence their dietary habits.
The findings, reported online in the journal Injury Prevention, are based on a survey of 1,878 teenagers aged 14 to 18 from 22 state schools in Boston.
The researchers, led by Dr Sara Solnick from the University of Vermont, wrote: "There was a significant and strong association between soft drinks and violence. There may be a direct cause-and-effect relationship, perhaps due to the sugar or caffeine content of soft drinks, or there may be other factors, unaccounted for in our analyses, that cause both high soft drink consumption and aggression."
A previous crime study recommended using tax and pricing policies to persuade young people to consume soft drinks instead of alcohol, the researchers noted. They added: "Our findings suggest that policies to encourage soft drink consumption may be a mistake."
British expert Prof Peter Kinderman, a clinical psychologist at the University of Liverpool, was critical of the study. He said: "The causes of violence in young people are complicated and this work is presenting an overly simplistic interpretation of the role of 'soft' drinks.
"There are a large number of known risk factors that would contribute to violent behaviour that have nothing to do with the consumption of these drinks.
"We know, in many areas of human behaviour that correlation does not imply causation. We also know that poor diet is associated with a range of negative health and social outcomes. This study is unsurprising.
"But, more importantly, it fails to address 'third-variable' issues that could explain the findings - kids exposed to different social, parental or educational backgrounds might therefore have different diets and different attitudes to aggression, without any direct causal link."