Research Activities早稲田大学 研究活動

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.

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.

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.

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.