Cognitive reserve, physical disorders and the trajectory of psychological and cognitive function.

BACKGROUND: Few studies have explored the association between cognitive reserve (CR) and the trajectory of psycho-cognitive function, particularly the interactive effect of physical disorders (PDs).

METHOD: Main analyses used data from middle-aged and older adults in the English Longitudinal Study of Ageing (ELSA), with replication using data from the US Health and Retirement Study (HRS). Latent class analysis was applied to classify participants based on baseline CR-related factors (education, occupation, stress, social engagement, physical activities, and marriage). Psycho-cognitive functions (depressive symptoms and global cognition) were measured during follow-up. Combinations of CR classifications and PDs were constructed. A linear mixed-effects model examined the relationships between CR classifications, PDs, and the progression of psycho-cognitive function, including within its specific domains.

RESULTS: 4918 middle-aged and older participants were included from the ELSA. A three-class latent model for CR classifications provided the best fit. Compared with the low CR group, the moderate and high CR groups showed better psycho-cognitive performance across all domains. Participants with PDs experienced significantly faster declines in psycho-cognitive function across all domains over time. No significant interactions between CR and PDs were found. However, those with low CR and PDs demonstrated significantly greater declines in cognitive function across all domains and increased depressive symptoms. The replication analysis, with 2175 participants from the HRS, largely supported the findings from the main analysis.

CONCLUSION: Higher CR mitigates the decline in psycho-cognitive function over time. A tendency for high CR to attenuate the overall decline in psycho-cognitive function associated with PDs was observed.