Depressive symptoms mediate the associations between air pollution exposure and anemia risk: a nationwide longitudinal study in China

Anemia remains a critical global health challenge, affecting 24.3% of the global population. While air pollution and depressive symptoms are recognized as potential risk factors, their combined effects and underlying mechanisms on anemia risk remain underexplored. This study aims to explore the associations between air pollution (PM₁, PM₂.₅ and O₃), depressive symptoms, and anemia risk using data from the China Health and Retirement Longitudinal Study. Data from 6,526 participants in the CHARLS database from 2011 to 2015 were analyzed. Air pollution exposure was assessed using geospatial modeling, while depressive symptoms were measured by the CESD-10 scale. Anemia was defined based on hemoglobin concentrations. Logistic regression models, restricted cubic spline analysis and mediating effect analysis were used to examine the relationships between air pollutants, depressive symptoms and anemia risk. Long-term exposure to PM₁ (OR = 1.12, 95% CI: 1.05–1.19, P < 0.001) and PM₂.₅ (OR = 1.10, 95% CI: 1.03–1.17, P = 0.004) was associated with elevated anemia risk, whereas O₃ exhibited a protective effect (OR = 0.68, 95% CI: 0.64–0.73, P < 0.001). Depressive symptoms mediated 5.6% of the PM₁-anemia association (P = 0.020) and 3.1% of the O₃-anemia pathway (P < 0.001). Stratified analyses revealed stronger PM-related anemia risks in rural residents (vs. urban) and western China (vs. eastern) while O₃’s protective effect was pronounced in populations with lower education or pre-existing digestive diseases. This study provides novel evidence that depressive symptoms partially mediate the effects of PM₁ and O₃ on anemia, underscoring the intertwined roles of environmental and mental health in hematological outcomes.