Fizzy drinks may make teenagers more aggressive. Research in the US suggests that teens who consumed at least five cans of cola or similar drinks a week were significantly more likely to have carried a gun or knife, or been involved in a fight, according to a study of 1,900 students aged between 14 and 18.

However, a UK expert dismissed the study as an "overly simplistic interpretation" of the role of fizzy drinks in violent behaviour. Peter Kinderman, professor of clinical psychology at the University of Liverpool, said: "The causes of violence in young people are complicated. There are a large number of risk factors that have nothing to do with the consumption of these drinks."

The study appears in the Injury Prevention journal.