**Background:** People experiencing homelessness (PEH) face accelerated aging and early onset of geriatric conditions, yet frailty—a validated predictor of age-related decline—has been understudied in this population. This rapid review synthesizes evidence on frailty prevalence and its cognitive, psychological, social, and structural determinants in adult PEH.
**Methods:** A rapid review was conducted following a streamlined systematic review methodology. Three databases (Medline, Embase, PsycINFO) were searched for primary research papers published between 2000–2021 studying PEH and frailty or frailty-related concepts. Two researchers independently screened 3,747 initial papers using Covidence software, with a third senior author resolving disagreements. Inclusion criteria required explicit use of a frailty measure/framework, measurement of cumulative geriatric syndromes with high conceptual overlap with frailty, or measurement of at least one physical geriatric deficit AND at least one psychological, cognitive, or social burden measure. Fourteen studies met criteria.
**Key Results:** Five studies used validated physical frailty measures; nine used cumulative deficit model constructs. All studies were cross-sectional or cohort designs, predominantly from anglophone countries (one from Peru). Average ages ranged from 39 to 72 years; female participation was low (only two studies >33% female).
*Prevalence:* Frailty rates in PEH ranged from 16% (Brown et al., Fried phenotype, mean age 56) to 55% (Rogans-Watson et al., Fried phenotype, mean age 56). Kiernan et al. found 23.3% frail by Clinical Frailty Scale (mean age 47). Salem et al. reported 54% frail by Frailty Index (mean age 52.4). In Rogans-Watson et al., PEH aged 56 had frailty scores equivalent to an 89-year-old in the general English population. Brown et al. found 16% frailty in PEH vs. 10% in the MOBILIZE Boston Study cohort (p<0.001). Compared to community-dwelling adults aged 65+ living in poverty, PEH (median age 58) had significantly higher rates of falls (33.7% vs. 21.9%), visual impairment (45.1% vs. 12.0%), urinary incontinence (48.0% vs. 29.5%), and depression (38.3% vs. 11.3%).
*Cognitive impairment:* Four studies reported high cognitive impairment rates: 49.1% scored ≤26 on MMSE (Rogoz & Burke); 66.4% had some degree of cognitive impairment on Pfeiffer's test (Moquillaza-Risco et al.); 65% impaired on MoCA with cut-off 26 (Mahmood et al.); and 68.1% scored below cut-off for verbal learning (Gicas et al.). Cognitive impairment was strongly associated with functional dependence—in Moquillaza-Risco et al., severe cognitive impairment predicted near-100% functional dependence at all ages. Gicas et al. found better inhibitory control associated with 6.6% decreased mortality risk, with the protective effect increasing by 0.3% per additional year of life.
*Psychosocial determinants:* Drug use was associated with 2.3 times higher total geriatric syndromes (Brown et al., 2013). Alcohol dependence was linked to greater impairment in learning, memory, and motor functions (Gicas et al., 2020). Among homeless veterans, substance use disorder diagnosis was elevated (ARR=2.18, 95% CI 2.05–2.31) compared to stably housed (Jutkowitz et al.). Loneliness prevalence was 39.6% in Patanwala et al., higher than general population estimates, and was independently associated with moderate-to-high physical symptom burden (AOR=2.32, 95% CI 1.26–4.28). Being female was associated with higher frailty (Kiernan et al., p=0.023) and functional dependence (Moquillaza-Risco et al.). Salem et al. (2013) found significant negative correlations between frailty and resilience (r=−0.395, p<0.01), social support (r=−0.377, p<0.01), and nutrition (r=−0.652, p<0.01); age, gender, healthcare utilization, nutrition, and resilience predicted 54.2% of frailty variance.
**Clinical Implications:** Service providers should recognize that PEH in their 40s and 50s can be frail and experience geriatric conditions. Early and frequent screening is warranted, with comprehensive assessment triggered by any single health presentation. Screening should include cognitive function, drug/alcohol use, and loneliness/social isolation. Holistic frailty measures like the Tilburg Frailty Indicator (TFI) and the Frailty Framework Among Vulnerable Populations (FFVP) show promise but require validation in PEH. Interventions should combine exercise, nutrition, housing strategies, and traditional geriatric services. Critically, these health interventions must complement—not substitute for—stable housing strategies. The review is limited by the cross-sectional nature of most included studies (precluding causal inference), variability in frailty definitions across studies, and potential confounding of cognitive assessments by high rates of mental illness and low literacy in PEH samples.