The effect of fish oil on physical aggression in schoolchildren — a randomized, double-blind, placebo-controlled trial

Abstract

Objectives The aim of the study was to investigate whether fish oil supplementation affected Japanese schoolchildren's behavior, with changes in aggression over time as the primary endpoint. Design and subjects A placebo-controlled double-blind study with 166 schoolchildren 9–12 years of age was performed. The subjects of the fish oil group ( n=83) took fish oil-fortified foods (bread, sausage and spaghetti). These foods were provided in amounts such that each subject in the fish oil group had an intake of 3600 mg of docosahexaenoic acid + 840 mg of eicosapentaenoic acid (EPA)/week for 3 months. The rest (the controls, n=83) took control supplements. At the start and end of the study, psychological tests were performed to assess their aggression. Results Physical aggression assessed by Hostility-Aggression Questionnaire for Children in girls increased significantly (median: 13 to 15, n=42) in the control group and did not change (13 to 13, n=43) in the fish oil group with a significant intergroup difference ( P=.008) with baseline as covariate. The changes in physical aggression scores over time and those of the ratio of EPA/arachidonic acid in RBC (ΔEPA/AA) were significantly correlated in girls who agreed to blood collection ( r=−.53, P=.01, n=23). On the contrary, there were no significant changes in physical aggression in boys. Aggression against others (extraggression) assessed by Picture Frustration Study did not change in the control group (median: 5 to 5) but increased significantly in the fish oil group (4 to 5) with a significant intergroup difference ( P=.02) with baseline as covariate. These changes in extraggression might be explained partly by significantly lower baseline values of extraggression in the fish oil group ( P=.02) than in the control group. There were no significant correlations between Δextraggression and ΔEPA/AA in blood-sampled children ( n=49). Impulsivity of girls assessed by parents/guardians using the diagnostic criteria for attention deficit/hyperactivity disorder of DSM-IV was reduced in the fish oil group (1 to 0) with a significant ( P=.008) intergroup difference from the control group (1 to 1). There were no significant correlations between Δimpulsivity and ΔEPA/AA in blood-sampled girls. In males, impulsivity reduced in both groups without any intergroup differences. Conclusion There is a possibility that changes in fatty acid nutrition might affect physical aggression especially in girls.