Apathy, dementia risk and mortality: long-term associations in a population-based prospective cohort of older adults

BackgroundUnderstanding whether apathy in older adults is related to incident dementia and mortality could help identify at-risk individuals, and inform public health efforts. This study aimed to investigate associations between apathy and these outcomes over long-term follow-up, and their independence from the overlapping symptoms of depression and fatigue. MethodsIn an Australian population-based cohort of 1,030 community-dwelling older adults aged 70-90, without dementia at baseline, apathy was assessed using the self-report Geriatric Depression Scale-3A subscale. Incident dementia was established via consensus diagnosis over 12 year follow-up, and mortality by record linkage over 18 years. We calculated hazard ratios (HRs) using Cox proportional hazards analyses. We repeated analyses adjusting for depression, fatigue and covariates, accounting for competing risk of mortality, and excluding short-term cases. FindingsUnadjusted primary analyses showed the presence of self-reported apathy was associated with higher risk of dementia (HR 1.45, 95% confidence interval (CI) 1.05-2.00) and mortality (HR 1.76, 95% CI 1.43-2.16). Participants with apathy developed dementia a year earlier, and died three years earlier. These findings remained significant when adjusting for depression. The association with dementia was no longer significant when adjusting for fatigue or covariates, nor when taking mortality into account or excluding those cases where dementia developed in the shorter term. InterpretationThe presence of apathy may represent an important risk indicator for dementia and mortality in older adults without dementia, independent of depression. Its association with dementia may reflect reverse causality. Future studies are needed to better understand the causal relationships that may underpin this observed association in the short and long-term, and the utility of apathy for screening in public health settings. FundingDementia Australia Research Foundation, Centre for Healthy Brain Ageing.