Association of brain pathology with the progression of frailty in older adults

Objective: We tested the hypothesis that brain pathology is associated with the rate of progression of physical frailty in older adults. Methods: A total of 791 older adults participating in the Religious Orders Study and Memory and Aging Project had annual clinical evaluations from which a previously established composite measure of physical frailty was derived and brain autopsy after death. A uniform neuropathologic examination included the assessment of macroinfarcts, microinfarcts, atherosclerosis, arteriolosclerosis, Alzheimer disease and Lewy body pathology, and nigral neuronal loss. Results: Mean follow-up before death was 6.4 years and age at death was 88.5 years. More than 95% of cases had evidence of one or more brain pathologies. In a linear mixed-effect model controlling for age, sex, and education, frailty increased at approximately 0.12 unit/year (estimate 0.117, SE 0.035, p>0.001). The rate of progression of frailty was accelerated with increasing age (estimate 0.002, SE 0.001, p=0.012). In separate models, the presence of macroinfarcts, Alzheimer disease and Lewy body pathology, and nigral neuronal loss was associated with a more rapid progression of frailty (all p values <= 0.010). When these 4 brain pathologies were considered together in a single model, Alzheimer disease pathology, macroinfarcts, and nigral neuronal loss showed independent associations with the rate of progression of frailty and accounted for more than 8% of the variance unexplained by demographic variables alone. Conclusion: The accumulation of common brain pathologies contributes to progressive physical frailty in old age.