Disability and co-morbidity in relation to frailty: how much do they overlap?

The purpose of this study was to examine the association of disability and co-morbidity with frailty in older adults. 2305 participants aged 65+ from the second wave of the Canadian Study of Health and Aging (CSHA), a prospective population-based cohort study, comprised the study sample. Following a standard procedure, two different frailty index (FI) measures were constructed from 37 deficits by dividing the recorded deficits by the total number of measures. One version excluded disability and co-morbidity items, the other included them. Time to death was measured for up to five years. Frailty was defined using either the frailty phenotype or a cut-point applied to each FI. Of people defined as frail using the frailty phenotype, 15/416 (3.6%) experienced neither disability nor co-morbidity. Using 0.25 as the cut-point score for the FI (without disability/co-morbidity) resulted in 101/1176 (8.6%) frail participants that had neither disability nor co-morbidity. Activities of daily living (ADL) limitations and co-morbidities occurred more often among people with the highest levels of frailty. The first ADLs to become impaired with increasing frailty were bathing, managing medication, and cooking with more than 25% of older adults with a FI score (without disability/co-morbidity) >0.22 experiencing dependency on them. The hazard ratio (HR) per 0.1 increase in FI score was 1.25 (95% CI: 1.20-1.30) when disability and co-morbidity were included in the index and 1.21 (1.16-1.25) when they were not included. In conclusion, disability and co-morbidity greatly overlap with other deficits that might be used to define frailty and add to their ability to predict mortality.