Background: While frailty is thought to be a wasting disorder, there is scarce data regarding the association between frailty and body mass index (BMI). The aim of this study was to determine the relationship between BMI, frailty, and mortality among hospitalized older adults.

Methods: This is a secondary analysis of a prospective cohort study of patients aged ≥65 years admitted to a tertiary center between 2014 and 2016. Frailty was assessed by Reported Edmonton Frailty Scale (REFS) and categorized as: not frail, vulnerable/mild frail, and moderate/severe frail. BMI (kg/m2) was categorized as: underweight (<18.5), normal (18.5-24.9), overweight (25.0- 29.9), or obese (≥ 30.0). Primary outcome was all-cause one-year mortality.

Results: Among 769 patients included in the study, 55.4% were frail. There was no statistically significant association between frailty categories and levels of BMI. Frail patients had a higher risk of death than non-frail after adjusting for confounders [HR: 1.98, 95% CI (1.46, 2.70) for mild frail and HR 2.03, 95% CI (1.43, 2.87) for moderate/severe frail]. Compared with normal weight patients, those who were overweight had a survival advantage if they were non-frail [HR 0.55, 95% CI (0.31, 0.96)] or vulnerable/mild frail [HR 0.65, 95% CI (0.43, 0.97)] but not if they were moderate/severe frail. There were no other statistically significant differences in survival by BMI and frailty categories.

Conclusions: We did not find a relationship between BMI and frailty among hospitalized older adults. Overweight patients had a survival advantage if they were non-frail or vulnerable. There is need for further longitudinal studies assessing the interaction between frailty and BMI in older adults.

Keywords: BMI; Frailty; Mortality; Reported Edmonton Frailty Scale.