A study of over 18,000 Boston public high school students show that those who were heavy soda drinkers were more prone to violent behavior. (And "heavy" in this context only means five or more sodas in a week.) Harvard study of teens links soft-drink consumption to violence
Other studies have linked soda consumption with depression and suicidal behavior, but Hemenway is not aware of anyone else studying the correlation with violent behavior. One further avenue for research is elucidating the underlying mechanism. It could be that a third variable, such as the quality of parenting, influences both soda consumption and aggressive behavior. (The researchers attempted to control for socioeconomic status and the quality of parenting; when they did, the correlation remained strong.) If there is a cause-effect relationship, the researchers speculate that excess caffeine and sugar (along with the subsequent blood-sugar crash) may leave soda drinkers irritable and prone to aggression; or maybe those who drink soda in place of healthier food miss out on nutrients that promote a calmer demeanor.