Association between Weight-Adjusted Waist Index and All-Cause Mortality in Depressed Individuals: A Cohort Study Based on NHANES (2005-2018)

Background: The relationship between the Weight - Adjusted Waist Index (WWI) and all - cause mortality in individuals with depression is unclear, and research on potential threshold effects is limited. This study explored the nonlinear association of WWI with all - cause mortality in this population. Methods: Leveraging data from the National Health and Nutrition Examination Survey (NHANES, 2005–2018), we conducted a cohort study of 3,667 depressed individuals. WWI was calculated as waist measurement divided by the square root of body mass. Cox proportional hazards models with restricted cubic spline functions evaluated dose - response associations and threshold impacts. Results: Participants' mean age was 47.88 years, mean follow - up was 87.83 months, and mortality rate was 13.01%. WWI had a U - shaped relationship with all - cause mortality (non - linearity, p < 0.05), with an inflection point at 17.94 cm/√kg. When WWI was below this threshold, a 1 - unit increase reduced mortality risk by 10% (HR = 0.90, 95% CI: 0.81 - 1.01). When WWI exceeded this threshold, each unit increased the risk by 21% (HR = 1.21, 95% CI: 1.13 - 1.30). Conclusion: Among depressed individuals, WWI had an inverted-U relationship with all-cause mortality, suggesting a threshold effect. These results emphasize the intricate interaction between abdominal adiposity and fatality in this group, necessitating further studies to verify the underlying mechanisms.