Does Longer Comprehensive Schooling Weaken the Association Between Genetic Predisposition and Mental Health? Evidence from Finland

Education is a key socioeconomic determinant of health that may mitigate the effects of genetic predisposition. This study examines whether Finland’s 1970s comprehensive school reform attenuated the association between polygenic scores (PGS) and psychiatric diagnoses and psychotropic medication use in adulthood. Using genetically informed register data for cohorts 1961–1965 (N = 3,936; 54.75% female), we exploit exogenous variation across municipalities and within birth years generated by the reform’s staggered rollout. Across 11 models, none of the overall reform-exposure × PGS interactions reached nominal statistical significance. Among women, one nominally significant interaction suggested that comprehensive schooling might have weakened the association between genetic predisposition to depression and later mental-health diagnoses, but it does not survive correction for multiple testing. However, the study had limited statistical power to detect small G×E interaction effects. We interpret these findings in light of previous studies from Finland, Sweden, the UK, and the US.