Occupational Cognitive Complexity in Earlier Adulthood Is Associated With Brain Structure and Cognitive Health in Midlife: The CARDIA Study

Objective: In line with cognitive reserve theory, higher occupational cognitive complexity is associated with reduced cognitive decline in older adulthood. How and when occupational cognitive complexity first exerts protective effects during the life span remains unclear. We investigated associations between occupational cognitive complexity during early to midadulthood and brain structure and cognition in midlife. Method: Participants were 669 adults from the Coronary Artery Risk Development in Young Adults study (aged 18-30 years at baseline, 52% female, 38% Black). We calculated scores reflecting occupational cognitive complexity using Census Occupation Codes (years 10 and 15) and Occupational Information Network (O*NET) data. At year 25, participants had structural brain magnetic resonance imaging, diffusion tensor imaging, and cognitive testing (Rey Auditory Verbal Learning Test, Digit Symbol Substitution Test, Stroop). In adjusted mixed models, we examined associations between occupational cognitive complexity during early to midadulthood and midlife brain structure, specifically gray matter volume and white matter fractional anisotropy, and cognition in midlife (all outcomes converted to z-scores). Results: Higher occupational cognitive complexity was associated with greater white matter fractional anisotropy (estimate = 0.10, p = .01) but not gray matter volume. Higher occupational cognitive complexity was associated with better Digit Symbol Substitution Test (estimate = 0.13, p < .001) and Stroop (estimate = 0.09, p = .01) performance but not Rey Auditory Verbal Learning Test performance. Conclusions: Occupational cognitive complexity earlier in adulthood is associated with better white matter integrity, processing speed, and executive function in midlife. These associations may capture how occupational cognitive complexity contributes to cognitive reserve. General Scientific Summary Cognitively stimulating activities, such as cognitively complex occupations, are thought to help prevent cognitive decline in aging. It is unclear how such activities benefit the brain and how early on during the life span protective effects first emerge. We found that individuals who had cognitively complex occupations in earlier adulthood had better brain health (specifically, white matter structure) and better cognitive health (specifically, processing speed, and executive function) in midlife. These associations may help explain why individuals who have cognitivel