The authors found a significant dose-response relationship between soda consumption and an overall measure of aggression (i.e., the higher soda intake, the more aggression). These aggressive behaviours include: destroying things belonging to others, getting into fights, and physically attacking people. Children with a high soda intake were also more likely to show attention problems and withdrawal.
This study does not tell us anything about the cause-effect relationship between soda consumption and problem behaviours because of its correlational, cross-sectional design. However, it indicates that a high soda intake play a role in problem behaviours, but many factors may be at stake.
Why would soda consumption lead to problem behaviours? Soft drinks contain sugars as well as caffeine. The authors emphasize that the scientific literature does not reveal much about the behavioural effects of sugar. In this study, high fruit juice consumption was associated with lower aggression, and high candy/sweets consumption was associated with higher levels of aggression.
Evidence has linked caffeine to a number of behavioural outcomes (e.g., insufficient sleep, nervousness, impulsivity and risk-taking in children and adolescents), and caffeine may therefore contribute to this study’s results (Suglia et al., 2013).
The study has a number of limitations besides its correlational design. First, it does not control for underlying conditions such as low blood sugar (low blod sugar may itself lead to aggression and higher soda intake).
Second, data on both soda consumption and behaviours are based on parent reports, and the size of soda serving and the type of soft drink are not defined. Finally, the study does not control for the children’s physical activity, violent video game watching and other dietary factors. For example, the authors note that food coloring agents have a potential negative impact on children’s behaviours.