Weight-adjusted waist index and cognitive impairment in older adults: A nationwide longitudinal cohort study

The association between adiposity and cognitive impairment remains inconclusive. This study aimed to evaluate the relationship between weight-adjusted waist index (WWI), a newly proposed indicator of adiposity, and cognitive impairment in a Chinese middle-aged and elderly population. Data from the 2011-2018 China Health and Retirement Longitudinal Study were used in this study. The WWI was calculated as waist circumference divided by the square root of body weight. Multivariate Cox regression models were employed to evaluate the association between WWI and cognitive impairment, while restricted cubic spline analysis was conducted to explore potential nonlinear associations between WWI and cognitive impairment. Model performance was assessed using Harrell's C-index, continuous net reclassification improvement, and integrated discrimination improvement to evaluate the incremental predictive value of WWI. The study included 5333 participants aged ≥45 years, comprising 2928 males (54.9%) and 2405 females (45.1%), with a mean age of 56.9 years (standard deviation = 8.2). During the 7-year follow-up, 1334 participants (25.0%) developed cognitive impairment. After adjusting for potential confounders, the WWI was positively associated with cognitive impairment (hazard ratio [HR] = 1.13, 95% confidence interval [CI]: 1.05-1.21, P < .001). Compared with the lowest quartile (Q1), participants in higher WWI quartiles exhibited an increased risk of cognitive impairment: Q2 (HR = 1.05, 95% CI: 0.89-1.24, P = .559), Q3 (HR = 1.13, 95% CI: 0.96-1.34, P = .144), and Q4 (HR = 1.26, 95% CI: 1.06-1.49, P = .009). Restricted cubic spline regression analysis demonstrated a positive linear relationship between WWI and cognitive impairment risk (P for nonlinearity = .678). Furthermore, the continuous NRI and integrated discrimination improvement for WWI demonstrated statistically significant improvements in predicting cognitive impairment compared with traditional adiposity metrics (both P < .05). The findings were further validated through a series of sensitivity analyses. This study demonstrates a significant association between higher WWI levels and an increased risk of cognitive impairment among middle-aged and older Chinese adults, suggesting that maintaining lower WWI levels may be associated with a lower risk of cognitive impairment.