Does prolonged education causally affect dementia risk when adult socioeconomic status is not altered? A Swedish natural experiment in 1.3 million individuals
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.
Seblova, D., M. Fischer, S. Fors, K. Johnell, M. Karlsson, T. Nilsson, A. Svensson, M. Lövdén and A. Lager (2021), Does prolonged education causally affect dementia risk when adult socioeconomic status is not altered? A Swedish natural experiment in 1.3 million individuals. American Journal of Epidemiology, 5, 817-826
DOI: 10.1093/aje/kwaa255