Influence of cognitive reserve on risk of depression and subsequent dementia: A large community-based longitudinal study.

Background: Cognitive reserve (CR) has been linked to dementia, yet its influence on the risk of depression and related outcomes remains unknown. We aimed to examine the association of CR with depression and subsequent dementia or death, and to assess the extent to which CR is related to depression-free survival.

Methods: Within the UK Biobank, 436,232 participants free of depression and dementia were followed. A comprehensive CR indicator (low, moderate, and high) was created using latent class analysis based on information on education, occupation, mentally passive sedentary behavior, social connection, confiding with others, and leisure activities. Depression, dementia, and survival status were ascertained through self-reported medical history and/or linkages to medical records. Data were analyzed using multi-state Markov model and Laplace regression.

Results: Over a median follow-up of 12.96 years, 16,560 individuals developed depression (including 617 with subsequent dementia) and 28,655 died. In multivariable multi-state models, compared with low CR, high CR was associated with lower risk of depression (hazard ratio 0.53 [95% confidence interval 0.51-0.56]) and lower risk of post-depression dementia (0.55 [0.34-0.88]) or death (0.69 [0.55-0.88]) in middle-aged adults (aged <60 years). In Laplace regression, the depression-free survival time was prolonged by 2.77 (2.58-2.96) years in participants with high compared to low CR.

Conclusions: High CR is associated with lower risks of depression and subsequent transitions to dementia and death, particularly in middle age. High CR may prolong depression-free survival. Our findings highlight the importance of enhancing CR in the prevention and prognosis of depression.