Longitudinal patterns and average burden of the weight-adjusted waist index-frailty index in relation to incident cardiovascular disease: a prospective cohort study of middle-aged and older adults in CHARLS

The weight-adjusted waist index (WWI) is a novel obesity indicator that reflects weight-independent abdominal obesity, whereas frailty reflects cumulative physiological decline and has been associated with adverse cardiovascular outcomes. However, the association of the combined WWI-frailty index (WWI-FI) with incident cardiovascular disease (CVD), as well as the longitudinal cardiovascular implications of average WWI-FI burden and directional changes in WWI-FI, remains unclear. This prospective study included 6,529 participants from the China Health and Retirement Longitudinal Study (CHARLS) who were free of CVD from 2011 to 2015 and had complete WWI and FI data at both time points. WWI-FI was calculated as the mean of standardized WWI and FI z scores. Participants were classified into four change patterns: low-low, low-high, high-low, and high-high. Average WWI-FI burden was analyzed as a standardized continuous variable and quartiles. Kaplan-Meier analysis, Cox proportional hazards models, and restricted cubic splines (RCS) were applied. During a mean follow-up of 5 years, 1,206 incident CVD events occurred. Compared with the low-low group, the fully adjusted HRs (95% CIs) were 1.83 (1.51–2.22) for low-high, 1.59 (1.19–2.11) for high-low, and 2.55 (2.14–3.02) for high-high patterns. Each 1-SD increase in average WWI-FI burden was associated with a higher CVD risk (HR 1.52, 95% CI 1.43–1.62). Participants in the highest quartile had a substantially higher risk than those in the lowest quartile (HR 3.32, 95% CI 2.72–4.04; P for trend < 0.001). RCS analysis showed a positive dose-response association with mild nonlinearity (P for nonlinearity = 0.0495). Competing-risk and sensitivity analyses yielded consistent results. Persistently high, unfavorable longitudinal changes, and greater average WWI-FI burden were associated with increased incident CVD risk. Repeated WWI-FI assessment may help identify individuals at elevated longitudinal cardiovascular risk. Clinical trial number: not applicable.