Does prolonged education causally affect dementia risk when adult socioeconomic status is not altered? A Swedish natural experiment on 1.3 million individuals

Abstract

Intervening on modifiable risk factors to prevent dementia is of key importance since progress-modifying treatments are not available. Education is inversely associated with dementia risk, but causality and mechanistic pathways remain unclear. We aimed to examine causality of this relationship in Sweden using a compulsory schooling reform that extended education by 1 year for 70 percent of the population as a natural experiment. The reform introduced substantial exogenous variation in education unrelated to pupils’ characteristics. We followed 18 birth cohorts (n=1,341,842) from 1985 to 2016 (until 79-96 years) for dementia diagnosis in the National Inpatient and Cause of Death Registers and estimated Cox survival models with stratified baseline hazards at the school-district level, chronological age as the time scale, and cohort indicators. Analyses indicated very small or negligible causal effects of education on dementia risk (main HR = 1.01; 95% CI: 0.98, 1.04). Multiple sensitivity checks considering only compliers, pre-post design, differences in healthcare-seeking behavior, and impact of exposure misclassification left the results essentially unaltered. The reform had limited effects on further adult socio-economic outcomes, such as income. Our findings suggest that without mediation through adult socioeconomic position, education cannot be uncritically considered as a modifiable risk factor for dementia.