Frailty Index and Cognitive Decline in Alzheimer's Disease: Data from the Impact of Cholinergic Treatment USe Study

**Objectives** To determine whether the Frailty Index (FI) was associated with short‐term cognitive decline (according to changes in Mini Mental State Examination (MMSE) and Alzheimer's Disease Assessment Scale–Cognitive subscale (ADAS‐Cog) scores at 1‐year follow‐up) in individuals with Alzheimer's disease (AD). **Design** Prospective cohort study. **Setting** Impact of Cholinergic Treatment USe study. **Participants** Individuals with mild‐to‐moderate AD (N = 973). **Measurements** Severity of dementia was assessed using the Clinical Dementia Rating (CDR). FI was calculated as the ratio of actual to potential deficits (deficits present divided by 30). Linear regression analyses were performed and stratified according to severity of dementia. Results A 1‐unit (0.033 points) increase in FI corresponded to significant and clinically relevant cognitive decline, after adjustments for age, sex, and years of education (0.63–4.63 points on the MMSE, P = .01; 2.87–11.1 points on the ADAS‐Cog, P = .001) after 1 year of follow‐up. Differences in changes in MMSE and ADAS‐Cog scores between nonfrail and frail individuals were 0.67 and 1.6 points, respectively. Although statistically significant, the clinical relevance of this finding remains to be further investigated. **Conclusion** The FI may be a promising instrument for the assessment of the vulnerability of individuals with AD. Its implementation in clinical practice may support clinical decisions by identifying individuals at high risk of negative outcomes, specifically, short‐term cognitive decline.