Physical frailty and cognitive frailty are two important targets of secondary intervention in aging research to narrow the gap between life and health span. The objective of the present narrative review was to examine clinical and epidemiological studies investigating the recently proposed construct of cognitive frailty and its subtypes, with a focus on operational definitions, clinical criteria, and emerging biomarkers potentially useful for the screening of this novel entity. Both physical frailty and frailty indexes with a multidimensional nature were associated with late-life cognitive impairment/decline, incident dementia, Alzheimer's disease (AD), mild cognitive impairment, vascular dementia, non-AD dementias, and AD pathology proposing cognitive frailty as a clinical entity with cognitive impairment related to physical causes with a potential reversibility. The new clinical and research AD criteria established by the National Institute on Aging-Alzheimer's Association and the American Psychiatric Association could improve the differential diagnosis of cognitive impairment within the cognitive frailty construct. The emerging biomarkers of sarcopenia, physical frailty, and cognitive impairment will provide the basis to establish more reliable clinical and research criteria for cognitive frailty, using different operational definitions for frailty and cognitive impairment and useful clinical, biological, and imaging markers for this novel clinical construct.
Keywords: Alzheimer’s disease; Biomarkers; Cognitive screening; Dementia; Frailty; Mild cognitive impairment.