Adiposity measures, body composition, and all-cause and cause-specific mortality in the Korean national health screening cohort: beyond body mass index.

While body mass index (BMI) is the most widely-used measure of adiposity, alternative measures, including waist circumference (WC), waist-to-height ratio (WHtR), weight-adjusted waist index (WWI), and a body shape index (ABSI), have been proposed to reflect body composition. However, the dose-response relationships between these alternative measures and mortality have not been fully established. We conducted a prospective cohort analysis using data from 328,084 Korean adults (aged ≥ 40 years) who participated in the national health screening program. Using Cox proportional hazards models, we examined the associations between multiple adiposity measures (BMI, WC, WHtR, WWI, ABSI) and all-cause and cause-specific mortality, with extensive control for methodological biases. During follow-up (mean: 10.2 years), 11,580 deaths were identified. BMI, WC, and WHtR showed J-shaped associations with all-cause, cardiovascular, and cancer mortality. The J-shaped associations became monotonically positive after adjustment for fat-free mass index (FFMI). WWI and ABSI showed monotonically positive associations with all-cause and cardiovascular mortality regardless of adjustment for FFMI, which remained unchanged after further control for methodological issues. All adiposity measures under study were positively associated with the proportion of "high fat-free/high fat mass" body type. However, with the proportion of "high fat-free/low fat mass" body type, WWI and ABSI were inversely associated, whereas BMI, WC, and WHtR presented inverse U-shaped associations. After accounting for fat-free mass, adiposity measures were associated with increased mortality among Korean adults in a monotonic dose-response manner. Our findings suggest that WWI and ABSI may reflect unhealthy body composition and could serve as alternative adiposity measures for clinical risk assessment.