Effects of education and occupational status on incident dementia: A COSMIC collaborative cohort study

Abstract

AbstractBackgroundEducation and occupational status are expected to protect against dementia, but the research findings have been inconsistent. This project aimed to examine 1) the unique contributions of education and occupational status to incident dementia, and 2) the mediating effects of occupational status on the association between education and dementia across diverse cohorts.MethodEducation and occupational status were harmonized as binary variables (education: ‘High school completion or above’ vs. ‘Less than high school completion; occupational status: ‘Mid to high status’ vs. ‘Low status’) due to the potential threshold effects and availability across datasets. Clinical diagnosis of dementia was used as an outcome. Using a Coordinated Analysis with 9 international datasets from 7 countries over 4 continents (Table 1; Australia, Germany, Italy, South Korea, Spain, and USA), the Cox proportional hazard regression model was applied to each dataset with participants’ age as the reference point, followed by meta‐analysis to provide the weighted summary effect sizes. Mediation analysis was conducted using the causal mediation approach with survival data (VanderWeele, 2011).ResultWe used data from 10,203 participants whose baseline age ranged from 58 to 103 years. Higher levels of education and occupational status were independently associated with decreased risk of incident dementia (Table 2; HR=0.70, 95% CI=[0.54, 0.92] for education; HR=0.79, HR=[0.66, 0.94] for occupational status). Heterogeneity across datasets was moderate for the education model (I 2=37%) and low for the occupation model (I 2= 0%). For the mediation analysis, the indirect effect was marginally significant (HR=0.94, 95% CI=[0.87, 1.00]) and 12% of the effect of education was mediated by occupational status.ConclusionUsing datasets from wide geographical regions, we found that both early life education and adulthood occupational status were independently predictive of incident dementia. Occupational status showed a weak mediating effect on the association between education and dementia. This finding suggests the importance of dementia prevention efforts in any stage of life course. Policy needs to prioritize early life education (possibly up to secondary education) and also target individuals with low occupational status to deliver dementia prevention and intervention.