Weight-adjusted waist index (WWI), a novel indicator of central obesity, has been suggested to be potentially associated with depression. Nevertheless, most available evidence comes from cross-sectional studies, and the direction, strength, and independence of this relationship across different populations remain uncertain. Specifically, there is a lack of large-scale longitudinal studies investigating this association in the Chinese middle-aged and elderly population.

To analyze the longitudinal association between the WWI and the risk of depression in middle-aged and older Chinese adults, providing a scientific basis for the prevention and intervention of depression in this population.

A longitudinal study design was adopted based on data from the China Health and Retirement Longitudinal Study (CHARLS) from 2011 to 2018. Depressive symptoms and anthropometric indicators were collected, and WWI was calculated as waist circumference divided by the square root of body weight . Logistic regression models were employed to examine the association between WWI levels and depression. Restricted cubic spline (RCS) curves were used to assess the dose-response relationship between WWI levels and depression risk. Subgroup analyses were conducted based on age, sex, obesity, smoking, and alcohol consumption to evaluate population heterogeneity. Finally, the predictive performance of WWI for depression was assessed using receiver operating characteristic (ROC) curves.

A total of 7 464 middle-aged and older adults were enrolled, with a median WWI of 11.06 (10.52, 11.62). Participants were stratified into four quartile groups based on WWI; the median WWI values for Q1 to Q4 were 10.14 (9.81, 10.35), 10.80 (10.66, 10.93), 11.31 (11.18, 11.46) and 12.04 (11.80, 12.45), respectively. During follow-up, the cumulative incidence of depressive symptoms was 47.11% (879/1 866), 47.21% (881/1 866), 49.25% (919/1 866) and 53.70% (1 002/1 866) across Q1-Q4. The incidence rose progressively with increasing WWI (P<0.05). Logistic regression indicated that, compared with those in the Q1 group, participants in the Q4 group had a 23% higher risk of depression (OR=1.23, 95%CI=1.05-1.44). RCS analysis revealed that the risk of depression increased with higher WWI levels, with each 1-unit increase in WWI associated with a 2% higher risk of depression (OR=1.02, 95%CI=1.00-1.04). Subgroup analysis showed that the association between WWI and depression risk was more pronounced in individuals aged <65 years (interaction P<0.05). ROC analysis indicated that WWI had better predictive value for depression than body fat index (AUC: 0.588 vs. 0.531; P<0.05), with an optimal cutoff value of 11.36 for increased depression risk.

Elevated WWI levels are associated with an increased risk of depression in middle-aged and older Chinese adults, particularly in those under 65 years of age. WWI may serve as a potential indicator for depression prevention and intervention strategies