Lifecourse investigation of the cumulative impact of adversity on cognitive function in old age and the mediating role of mental health: longitudinal birth cohort study.

OBJECTIVE: To investigate the accumulation of adversities (duration of exposure to any, economic, psychosocial) across the lifecourse (birth to 63 years) on cognitive function in older age, and the mediating role of mental health. DESIGN: National birth cohort study. SETTING: Great Britain. PARTICIPANTS: 5362 singleton births within marriage in England, Wales and Scotland born within 1 week of March 1946, of which 2131 completed at least 1 cognitive assessment. MAIN OUTCOME MEASURES: Cognitive assessments included the Addenbrooke's Cognitive Examination-III, as a measure of cognitive state, processing speed (timed-letter search task), and verbal memory (word learning task) at 69 years. Scores were standardised to the analytical sample. Mental health at 60-64 years was assessed using the 28-item General Health Questionnaire, with scores standardised to the analytical sample. RESULTS: After adjusting for sex, increased duration of exposure to any adversity was associated with decreased performance on cognitive state (ß=-0.39; 95% CI -0.59 to -0.20) and verbal memory (ß=-0.45; 95% CI -0.63 to -0.27) at 69 years, although these effects were attenuated after adjusting for further covariates (childhood cognition and emotional problems, educational attainment). Analyses by type of adversity revealed stronger associations from economic adversity to verbal memory (ß=-0.54; 95% CI -0.70 to -0.39), with a small effect remaining even after adjusting for all covariates (ß=-0.18; 95% CI -0.32 to -0.03), and weaker associations from psychosocial adversity. Causal mediation analyses found that mental health mediated all associations between duration of exposure to adversity (any, economic, psychosocial) and cognitive function, with around 15% of the total effect of economic adversity on verbal memory attributable to mental health. CONCLUSIONS: Improving mental health among older adults has the potential to reduce cognitive impairments, as well as mitigate against some of the effect of lifecourse accumulation of adversity on cognitive performance in older age.