Association of body indices with mortality in older population: Japan Specific Health Checkups (J-SHC) Study

Background: Obesity indices reflect not only fat mass but also muscle mass and nutritional status in older people. Therefore, they may not accurately reflect prognosis. This study aimed to investigate associations between a body shape index (ABSI), body mass index (BMI), and mortality in the general older population.

Methods: This nationwide observational longitudinal study included individuals aged between 65 and 74 years who underwent annual health checkups between 2008 and 2014. Exposures of interest were ABSI and BMI, and the primary outcome was all-cause mortality. Association between the ABSI and BMI quartile (Q1-4) and mortality was assessed using Cox regression analysis. A restricted cubic spline was also used to investigate nonlinear associations. The missing values were imputed using multiple imputation by chained equations.

Results: Among 315,215 participants, 5074 died during a median follow-up period of 42.5 (interquartile range: 26.2-59.3) months. Compared with ABSI Q1, ABSI Q3 and Q4 were associated with increased risk of mortality, with the adjusted hazard ratios (aHRs) and 95% confidence intervals (CIs) of 1.13 (1.05-1.22) and 1.23 (1.13-1.35), respectively. Compared with BMI Q3, BMI Q1 and Q2 were associated with an increased risk of mortality, with aHRs and 95% CIs of 1.51 (1.39-1.65) and 1.12 (1.03-1.22), respectively. The impacts of these indices were greater in male than in female. The heatmap of the aHR for mortality by continuous ABSI and BMI showed that higher ABSI was consistently associated with higher mortality risk regardless of BMI, and that the combination of low BMI and high ABSI was strongly associated with increased mortality risk.

Conclusions: High ABSI and low BMI are additively associated with the risk of all-cause mortality in the general older population in Japan. Combination of ABSI and BMI is useful for evaluating mortality risk in older people.