The Influence of Zinc Supplementation on Improving Learning Concentration and Hemoglobin Levels in Anemic Adolescent Girls at Junior High School

Mild to moderate anemia impairs cognitive performance and academic engagement among adolescent girls, yet school-based nutrition programs in Indonesia focus largely on iron and vitamin A. This study evaluated whether a focused 30-day regimen of 20 mg/day zinc could improve both hemoglobin concentration and attention, as measured by the Stroop Color–Word Test, in 30 junior high school girls with baseline hemoglobin < 12 g/dL. Following daily supplementation, mean hemoglobin rose from 10.6 ± 0.5 g/dL to 12.4 ± 0.4 g/dL (Δ = 1.8 g/dL, p < 0.001, Cohen’s d = 3.86), fully eliminating moderate anemia in this cohort. Stroop scores increased from 61.2 ± 5.3 to 75.8 ± 4.6 points (Δ = 14.6, p < 0.001, Cohen’s d = 2.88), with no students remaining in the lowest concentration category post-intervention. These parallel gains reflect zinc’s dual role in enhancing erythropoiesis improving cerebral oxygen delivery and modulating neurotransmission via NMDA/GABA balance and BDNF upregulation. Effect sizes exceed those typically reported for iron-only or broader micronutrient interventions. Findings support integrating a one-month zinc supplement into Indonesian school-health protocols to rapidly correct anemia and bolster cognitive readiness for learning.