Education, Occupational Complexity, and Incident Dementia: A COSMIC Collaborative Cohort Study

Abstract

Background: Education and occupational complexity are main sources of mental engagement during early life and adulthood respectively, but research findings are not conclusive regarding protective effects of these factors against late-life dementia.

Objective: This project aimed to examine the unique contributions of education and occupational complexity to incident dementia, and to assess the mediating effects of occupational complexity on the association between education and dementia across diverse cohorts.

Method: We used data from 10,195 participants (median baseline age = 74.1, range = 58∼103), representing 9 international datasets from 6 countries over 4 continents. Using a coordinated analysis approach, the accelerated failure time model was applied to each dataset, followed by meta-analysis. In addition, causal mediation analyses were performed.

Result: The meta-analytic results indicated that both education and occupational complexity were independently associated with increased dementia-free survival time, with 28%of the effect of education mediated by occupational complexity. There was evidence of threshold effects for education, with increased dementia-free survival time associated with 'high school completion' or 'above high school' compared to 'middle school completion or below'.

Conclusion: Using datasets from a wide range of geographical regions, we found that both early life education and adulthood occupational complexity were independently predictive of dementia. Education and occupational experiences occur during early life and adulthood respectively, and dementia prevention efforts could thus be made at different stages of the life course.

Keywords: Cognitive reserve; coordinated analysis; education; occupational complexity.

Figure 1.. Sample selection.

*Data for EAS and MYHAT were subdivided into Whites and Blacks to account for potential heterogeneity; thus EAS and MYHAT participants identified with races other than Whites and Blacks were excluded.

Figure 2.

The mediation model among education, occupational complexity, and dementia. The solid line indicates natural direct effect, and the dotted line represents the mediated, indirect effect. The exposure-mediator interaction was not included because results from preliminary analysis did not find evidence of interaction.

Figure 3.

Effects of education on dementia-free survival time. Model 1 controlled for sex and baseline age, and Model 2 further controlled occupational complexity. Effects were not estimated for 'Above HS' of MYHAT Black due to the insufficient sample size.

Figure 4.

Effects of occupational complexity on dementia-free survival time. Model 1 controlled for sex and baseline age, and Model 2 further controlled for education. Effects were not estimated for 'High' of KLOSCAD due to the insufficient sample size.