Association between Nutritional and Physical Factors and Anemia among Schoolchildren Aged 5 to 11 Years in Beijing
This study examines the relationship between nutritional, biochemical, and physical factors and anemia in a population of 5- to 11-year-old schoolchildren in Beijing. While anemia in children is often attributed to micronutrient deficiencies, research in well-off regions has been limited. This work leverages a 2015 cross-sectional survey, Nutrition and Health Surveillance in Schoolchildren of Beijing, to explore underlying causes beyond traditional nutritional deficiencies.
Study Design and Methodology
Data were derived from three nested study populations within the broader surveillance project. Study Population 1 included 4,326 participants with sociodemographic and anthropometric data. Study Population 2 (1,969 participants) expanded this dataset with biochemical markers, including hemoglobin (Hb), serum ferritin (SF), folate, vitamin B12, vitamin A, zinc, and inflammatory markers. Study Population 3 comprised 554 children with detailed 3-day dietary recall records. Exclusion criteria removed individuals with incomplete data, recent infections, or conditions affecting nutritional status.
Hemoglobin levels were measured using the Hemocue system. Anemia was defined as Hb <115 g/L for children aged 5–11 years. Iron deficiency (ID) was classified as SF <15 μg/L, and iron deficiency anemia (IDA) required both anemia and ID. Folate deficiency was defined as serum folate <4 ng/mL, vitamin B12 deficiency as serum B12 <203.25 pg/mL, and vitamin A deficiency as serum retinol <0.7 μmol/L, per World Health Organization (WHO) and Chinese guidelines. Anthropometric metrics, including height-for-age Z-scores (HAZ) and BMI-for-age Z-scores (BAZ), were calculated using WHO growth standards.
Key Findings
Prevalence of Anemia and Nutritional Deficiencies
The overall anemia prevalence was 2.8% (56 cases), with no significant gender disparity (44.6% boys vs. 55.4% girls, P = 0.38). Rural children constituted 85.7% of anemia cases (P < 0.01). Mean Hb levels were 128.9 ± 9.5 g/L, consistent across sexes. ID and IDA rates were strikingly low at 0.7% and 0.2%, respectively. Among anemic children, only three cases were linked to IDA. No folate, vitamin B12, or vitamin A deficiencies were observed in anemic participants. The general population showed minimal deficiencies: vitamin A (0.2%), vitamin B12 (0.2%), and folate (0.6%).
Anthropometric and Demographic Correlates
Anemic children exhibited significantly lower height and weight compared to non-anemic peers (P < 0.01). Younger age, rural residency, and lack of nutritional supplements were associated with higher anemia risk (P < 0.05). Scatterplots (Supplementary Figure 2) illustrated that only four anemic children had HAZ scores below −1 (indicating mild stunting), with one child scoring −2.14 (moderate stunting). However, these stunted cases lacked concurrent micronutrient deficiencies. For example, the child with HAZ −2.14 had normal SF and vitamin B12 levels but marginally low folate (4.21 ng/mL).
Dietary Intake and Biochemical Associations
Analysis of dietary intake (Study Population 3) revealed no significant differences in energy, macronutrient, or micronutrient consumption between anemic and non-anemic groups (P > 0.05). However, age, rural residence, and lower anthropometric indices remained linked to anemia (P < 0.05). Multivariable linear regression for Study Population 2 (excluding three IDA cases) identified age (β = 1.517, P < 0.001), HAZ (β = 0.657, P = 0.002), BAZ (β = 0.398, P = 0.036), serum vitamin A (β = 2.176, P = 0.001), and zinc (β = 0.369, P = 0.006) as positive predictors of Hb. Soluble transferrin receptor (sTfR), a marker of iron demand, negatively correlated with Hb (β = −0.459, P = 0.021). Interestingly, dietary vitamin A and zinc intake did not correlate with Hb in Study Population 3, suggesting physiological or absorption factors outweigh dietary intake.
Stratified Analysis by Age Tertiles
Further stratification of Study Population 1 into age tertiles (Supplementary Table 4) showed progressive increases in height, weight, and Hb with age (P < 0.05). Regression models confirmed age (β = 1.501, P < 0.001), female sex (β = 0.579, P = 0.038), HAZ (β = 0.814, P < 0.001), BAZ (β = 0.301, P = 0.008), and rural residence (β = −1.014, P = 0.001) as independent Hb predictors. Follow-up data from 2017 indicated that most children with anemia in 2015 had recovered without intervention, underscoring age-related physiological resolution.
Discussion
Rethinking Nutritional Determinants
Contrary to global trends where ID is a primary anemia driver, this study highlights minimal contributions from iron or vitamin deficiencies in Beijing’s schoolchildren. The low IDA prevalence aligns with prior research in non-malarious, urban Asian settings, where dietary iron sufficiency and low infection rates reduce ID risk. Plant-based diets, often criticized for low iron bioavailability, were not associated with anemia in this population, mirroring findings from the China Health and Nutrition Survey.
Growth Status and Developmental Delays
The strong association between lower Hb and younger age or stunted growth suggests physiological rather than pathological mechanisms. Younger children may have transiently lower Hb due to rapid growth outpacing blood volume expansion. This aligns with longitudinal data showing spontaneous resolution of mild anemia in early childhood. The link between HAZ/BAZ and Hb further implies that children with delayed growth trajectories may exhibit temporary Hb deficits, which normalize as they catch up developmentally.
Limitations and Public Health Implications
The cross-sectional design precludes causal inferences, and unmeasured confounders (e.g., menstruation, helminthiasis, genetic hemoglobinopathies) may influence results. Nevertheless, the findings argue against blanket iron supplementation in similar populations. Instead, policymakers should prioritize growth monitoring and nutritional education to support balanced diets. Schools and health systems could integrate Hb and anthropometric tracking into routine checkups, particularly for rural and younger children.
Conclusion
In Beijing’s schoolchildren, anemia is largely independent of classical micronutrient deficiencies, with age and physical development serving as primary determinants. Public health strategies should emphasize developmental surveillance and holistic nutritional support over micronutrient supplementation in low-prevalence settings.
doi.org/10.1097/CM9.0000000000001600
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