Pathways to frailty and its adverse outcomes: evidence from the English longitudinal study of ageing

Frailty affects 10% of adults aged 65 years and older. It denotes loss of an individual’s body reserves, which increases vulnerability to developing adverse health outcomes such as death, disability, and institutionalization. Consequently, frailty has been described as the most problematic expression of ageing. Having good understanding of specific conditions influencing development of frailty and its effects holds the key to slowing its progression and mitigating its adverse outcomes. To this end, pathways to frailty and its adverse outcomes are the focus of my thesis. I begin with a literature review to assemble evidence on frailty pathways and instruments. Guided by this evidence and using the working framework of the Canadian Initiative on Frailty and Aging as the template, frailty pathways incorporating physical, psychological, and social conditions are conceptualized. Arguing that narrower physical frailty specifications are more suitable for investigating these pathways, I develop them based on the frailty phenotype. In my first two papers, I use data of 4,638 respondents aged 65 to 89 years from the English Longitudinal Study of Ageing to demonstrate construct, concurrent, and predictive validity of two physical frailty specifications. Adopting the specification with three indicators for latent growth curve analysis in my third paper, I show that chronic disease, allostatic load, low physical activity, cognitive impairment, depressive symptoms, poor social support, and poor social integration are predictors, mediators, or moderators on pathways to physical frailty. In my fourth paper, discrete time survival analysis reveals that low physical activity and cognitive impairment are mediators on pathways from physical frailty to death. In my fifth paper, autoregressive cross-lagged analyses demonstrate that these two conditions and depressive symptoms are mediators on pathways from physical frailty to activity limitation. All these conditions represent potentially modifiable targets for population-level interventions to address physical frailty in older people