Longitudinal Associations Between Weight-Adjusted Waist Index and Cognition in Middle-Aged and Older Adults in China

Obesity is associated with cognitive decline, yet evidence regarding the role of different obesity indices is heterogeneous. This study aims to investigate the impact of the weight-adjusted waist index (WWI), an indicator providing an optimised assessment of abdominal obesity, on cognition in middle-aged and older adults in China.

We used data from five waves of the China Health and Retirement Longitudinal Study (2011-2020). Global cognition function was divided into two dimensions: fluid and crystallised cognitive function. The scores were adjusted for comparability (across the 2018 and 2020 waves) and standardised. Restricted cubic splines assessed the potential nonlinear relationship between WWI and cognition. Linear mixed effects models examined longitudinal associations between WWI and cognitive function and delineated the age-related cognitive trajectories between different WWI subgroups.

Totally, 8240 individuals aged over 50 years at baseline were enrolled (mean age 61.12 ± 7.45 years), corresponding to 32 498 observations. Nonlinear relationship between WWI and global cognition was found with an inflection point at the standardised WWI value of -0.2 (11.04 cm/ $\sqrt{\mathrm{kg}}$ ; p-non-linear = 0.026). Each one-SD increase in WWI was linked to lower cognitive scores: global cognition (β = -0.064; 95% CI: -0.089, -0.038), fluid cognition (β = -0.064; 95% CI: -0.089, -0.038), crystallised cognition (β = -0.046; 95% CI: -0.070, -0.022). Compared with the lowest tertile (T1), the highest WWI tertile (T3) had lower baseline cognitive scores and a faster age-related cognitive decline. Over 10 years, a cumulative difference of 0.123 SD in global cognition was observed between individuals with a 1-SD difference in WWI, and those in the T3 group showed a cumulative deficit of 0.141 SD compared to the T1. This pattern was more pronounced for fluid cognitive function.

Results indicated that higher WWI was significantly associated with lower cognitive scores. Moreover, in the highest WWI tertile, cognitive function exhibited a higher rate of decline. It is imperative to implement public health measures promoting effective abdominal obesity control strategies, thereby mitigating the burden of dementia.