Abstract
BACKGROUND: Sedentary behavior and obesity are established risk factors for depression. The weight-adjusted-waist index (WWI) is a more accurate obesity measure than body mass index (BMI) or waist circumference (WC). This study aims to investigate if WWI mediates the effect of sedentary behavior on depression. METHODS: Data on daily sitting times, WWI and depression symptoms assessed by the Patient Health Questionnaire-9 (PHQ-9) scores were analyzed for this study. WWI was calculated as WC divided by the square root of body weight. Depression was defined as a PHQ-9 score ≥ 10. We used weighted logistic regression and restricted cubic splines (RCS) to examine the linear and nonlinear effects of daily sitting time and WWI on depression. Mediation analysis was performed to determine if WWI mediates the relationship between daily sitting time and depression. Gender-stratified analysis was also conducted. RESULTS: The study included 26,508 participants. Adjusted analyses showed positive associations of both daily sitting time (OR = 1.035, 95 % CI 1.015-1.056) and WWI (OR = 1.345, 95 % CI 1.226-1.476) with depression. Sitting > 8 h/day conferred higher depression risk versus < 4 h/day (OR = 1.268, 95 % CI 1.086-1.481). Similarly, the highest WWI quartile (Q4) had significantly greater risk than the lowest (Q1) (OR = 1.791, 95 % CI 1.429-2.245). WWI significantly mediated the sitting-depression relationship (proportion mediated: 0.075, 95 % CI 0.062-0.212, P < 0.001). CONCLUSION: Sedentary behavior and WWI both elevate depression likelihood. Furthermore, WWI partially mediates the effect of sedentary behavior on depression, and this mediation effect is independent of gender.