Abstract

Several observational studies indicate that dietary habits in children and adolescents are associated with school performance. These associations are heavily confounded by socio-economic characteristics, such as household income and parents educational attainment, amongst other factors. In this study, we report observational and causal effects of habitual diet on school performance, using individual level data for 9,220 adolescents in the Northern Finland Birth Cohort 1986. For this purpose, we derived principal components for the dietary variables, meal patterns and school performance variables. The observational study showed a significant association of consumption of foods that are high in fat, salt and sugar (HFSS) with poor performance in all school subjects, and an association of consumption of healthy foods and traditional foods with good school performance in general subjects, science and physical education (PE). Moreover, a positive association was observed between not skipping breakfast and good performance in all school subjects. Mendelian randomisation analysis confirmed a negative effect of HFSS on school performance in general/science subjects (-0.080, -0.128 to -0.033) and a positive effect of healthy food on school performance in general/science subjects (0.071, 0.024 to 0.119) and PE (0.065, 0.021 to 0.110). To conclude, we identified compelling evidence that HFSS foods and healthy foods were causally affecting school performance.