Exposure to air pollutants is associated with adverse changes in hemoglobin trajectories and an increased risk of anemia in children and adolescents.
BACKGROUND Air pollution is associated with anemia in children, however, longitudinal data supporting this association are insufficient. METHODS From 2019 to 2023, we conducted a dynamic cohort study involving 33,900 participants from 119 primary and secondary schools across 16 districts in Shanghai. We obtained the daily average concentrations of five air pollutants (PM2.5, O₃, NO₂, SO₂, and CO) based on school addresses using the China High Air Pollutants (CHAP) dataset to assess the exposure levels of the study subjects. We used latent class mixed models to determine the longitudinal trajectories of hemoglobin (Hb) and multinomial logistic regression models to estimate odds ratios (ORs) and 95% confidence intervals (CIs) between trajectory categories. Linear and logistic regression models were used to evaluate the associations between air pollutant exposure level and Hb and anemia risk, respectively, and Cox regression models was used for longitudinal validation. Interaction terms for gender, age, and body mass index (BMI) were used to explore the modifying effects of these factors. RESULTS At the baseline survey, 3,213 students (9.48%) were identified as anemic, with a higher proportion of girls (63.8%). During an average follow-up period of 3.16 years, 1,685 participants (4.9%) were observed to develop anemia. Children's hemoglobin levels showed three different trajectory patterns throughout the study period. Exposure to PM2.5 [OR (95% CI) = 2.124(1.853, 2.433)] was associated with adverse trajectory changes characterized by "low hemoglobin". Longitudinal analysis shows that exposure to PM2.5 [HR = 1.213, 95% CI: (1.068, 1.376)], NO2 [HR = 1.409, 95% CI: (1.254, 1.584)], and SO2 [HR = 1.268, 95% CI: (1.172, 1.372)] is associated with an increased risk of anemia. Stratified analysis showed that the adverse effects of PM2.5 exposure on anemia were more pronounced in younger or underweight children. The adverse effects of NO2 exposure on anemia were more significant in older or obese children. The association between SO2 exposure and the impact on anemia mainly appeared in male or younger children. CONCLUSIONS Long-term exposure to air pollutants is associated with an increased burden of anemia in children and adolescents, and attention should be focused on vulnerable groups such as girls and underweight children.