Sleep Duration and the Association Between Systemic Inflammatory Response Index and Depressive Symptoms Among Emerging Adults: Evidence from NHANES 2005-2023

Objective This study examined the association between the Systemic Inflammatory Response Index (SIRI) and depressive symptoms among emerging adults aged 18-25 years, with an emphasis on the indirect role of sleep duration. Method This cross-sectional study utilized data from the National Health and Nutrition Examination Survey (NHANES) 2005-2023. A total of 6563 participants with complete data on the Patient Health Questionnaire-9 (PHQ-9), complete blood count parameters for SIRI calculation, and self-reported sleep duration were included. Depressive symptoms were defined as a PHQ-9 score ≥10. Weighted multivariable logistic regression, restricted cubic spline analysis, and bootstrap-based exploratory mediation analysis (n = 1000) were employed. Results Overall, 604 participants (9.2%) met the criteria for depressive symptoms. After full adjustment for covariates, SIRI demonstrated a significant positive association with depressive symptoms (Model 4: OR = 1.16, 95% CI = 1.02-1.33, P = 0.03). Participants in the highest SIRI quartile (Q4) exhibited 33% higher odds of depressive symptoms compared to the lowest quartile (Q1) (OR = 1.33, 95% CI = 1.09-1.61, P = 0.005). No significant nonlinearity was observed (P for nonlinearity = 0.066). Exploratory mediation analysis revealed a negative indirect effect through sleep duration (β = −0.009), accounting for approximately 6.2% of the total effect. Conclusions Higher SIRI levels were associated with increased odds of depressive symptoms among emerging adults. Sleep duration played a modest suppressor role in this relationship, suggesting complex interactions between inflammation, sleep, and mental health warranting further investigation through prospective studies.