Iron Supplementation in Early Childhood and the Spectrum of Neurocognitive Development: A Systematic Review and Meta-Analysis

Introduction: Iron deficiency during pregnancy and early childhood may affect myelination, neurotransmission, and neural network maturation, with potential consequences for motor, cognitive, and language development. Objective: To quantitatively synthesize the effects of iron supplementation on motor, cognitive/global, and language development by integrating the original dataset with a complementary search for original studies. Methods: Systematic review with random-effects quantitative synthesis. The expanded review included 11 publications. Continuous outcomes and adjusted estimates were harmonized to log odds ratios (logOR), with positive values indicating better performance with greater iron exposure. Between-study variance was estimated by restricted maximum likelihood (REML). Ten motor, 11 cognitive/global, and 7 language effect estimates were pooled. Results: For motor development, the pooled effect was logOR 0.31 (95% CI 0.14 to 0.48; OR 1.36; p < 0.001; τ² = 0.044; I² = 69.3%). For cognitive/global development, the pooled effect was logOR 0.11 (95% CI -0.10 to 0.33; OR 1.12; p = 0.307; τ² = 0.088; I² = 74.8%). For language, the pooled effect was logOR -0.02 (95% CI -0.26 to 0.21; OR 0.98; p = 0.851; τ² = 0.048; I² = 50.7%). Conclusion: The expanded synthesis yielded a positive pooled estimate for motor development, whereas pooled cognitive/global and language estimates remained close to the null. Effect magnitude and direction varied across populations, timing and dose of supplementation, baseline iron status, and age at assessment.