Frailty and Cognitive Impairment: Time to Acknowledge and Embrace Heterogeneity

Frailty and cognitive impairment, two common geriatric conditions, are known to be associated with late-life vulnerability in older adults (Todd et al., 2013; Cesari et al., 2016; Fried et al. 2001). An estimated 15% of non-nursing home older adults in the United States aged 65 and over are frail (Bandeen-Roche et al., 2015), and about 22% and 9% have mild cognitive impairment and dementia (Katz et al. 2012; Langa et al., 2017). Physical frailty and cognitive impairment often co-exist in older adults. However, there are sizeable subgroups who have one but not the other. According to a recent US population-based study published in the Journal of the American Geriatrics Society by Ge and colleagues (Ge et al., 2020), 67% of frail older adults had cognitive impairment, and 29% of older adults with cognitive impairment were frail. That physical frailty and cognitive impairment may not manifest together is reinforced by clinical encounters with older adults who are physically robust but cognitively frail and vice versa. 

The study by Ge et al. also found that individuals with frailty only (meaning without cognitive impairment) had the highest prevalence of obesity, current smoking, multimorbidity, lung disease, and history of surgery. The group with both cognitive impairment and frailty were the oldest on average and had the highest prevalence of dementia, depression, cardiovascular diseases, and disability. It is also worth noting that the prevalence of dementia in the group with both frailty and cognitive impairment was more than doubled compared to the group with cognitive impairment alone. This latter finding makes it plausible that the comorbid status could result from frailty being a sequela of cognitive impairment beyond a certain severity. Alternatively, the joint versus separate occurrence of frailty and cognitive impairment may signal different etiologies and pathways. Preliminary support of the latter came from a recent longitudinal study showing that people on a trajectory to develop dementia were three times more likely to experience concurrent onset of frailty and cognitive impairment than to develop cognitive impairment first (Chu et al., 2019). Taken together, these findings suggest that the co-occurrence of cognitive impairment and frailty may be driven primarily by neurologic pathologies rather than “normal” cognitive aging or physical impairments. By contrast, the group with cognitive impairment only may represent mostly normal cognitive aging with less disease burden, as shown in the study by Ge et al.

The findings above support the value of assessing frailty and cognitive impairment in tandem in clinical settings in order to achieve greater measurement specificity as well as inform the selection and prioritization of treatment targets. For example, the group with frailty only may benefit from tailoring interventions based on specific disease profiles. In contrast, the group with cognitive impairment only may largely reflect non-pathological cognitive aging given their lower dementia prevalence and multimorbidity burden (cardiovascular diseases in particular), and therefore may benefit from lifestyle interventions. The group with comorbid frailty and cognitive impairment on the other hand may benefit from interventions that target both dementia-related pathologies and vascular risk factors to slow down the progression of dementia and the accompanying diseases. Now is the time to embrace a paradigm shift from pursuing research on frailty and cognitive impairment in silos to an integrative and holistic approach by which precision medicine can succeed in caring for older adults.