Frailty modifies the association of body mass index with mortality among older adults: Kyoto-Kameoka study.

ABSTRACT

BACKGROUND & AIMS: The differences in the association of body mass index (BMI) with mortality between older adults with and without frailty remain unclear. This study investigated this association in community-dwelling older adults with and without frailty. METHODS: This prospective study included 10,912 adults aged ≥65 years who provided valid responses to a baseline mail survey questionnaire in the Kyoto-Kameoka Study in Japan. The BMI was calculated based on self-reported height and body weight and classified into four categories <18.5, 18.5-21.4, 21.5-24.9, and ≥25.0 kg/m2. Frailty was evaluated using the validated Kihon Checklist and defined as a score of 7 or higher out of a possible 25 points. Mortality data were collected from 30 July 2011 to 30 November 2016. Hazard ratios (HR) for all-cause mortality were calculated using a multivariable Cox proportional hazards model. RESULTS: During the 5.3 year median follow-up period (54,084 person-years), 1352 deaths were recorded. After adjusting for confounders, including lifestyle and medical history, compared with participants with a BMI of 21.5-24.9 kg/m2, those in the lower BMI category had a higher mortality HR, while those with a higher BMI displayed an inverse association with mortality (<18.5 kg/m2 HR 1.85, 95% confidence interval [CI] 1.58-2.17; 18.5-21.4 kg/m2 HR 1.38, 95% CI 1.21-1.58; and ≥25.0 kg/m2 HR 0.80, 95% CI 0.67-0.96). In a model stratified by frailty status, the BMI range with the lowest HR for mortality was 23.0-24.0 kg/m2 in non-frail older adults; however, in frail older adults, a higher BMI was inversely associated with mortality. CONCLUSIONS: The relationship between BMI and mortality varies between individuals with and without frailty, with those experiencing frailty potentially benefiting from a higher BMI compared to those without frailty. This study suggests that frailty should be assessed when considering the optimal BMI for the lowest mortality risk among older adults.