Effect of Vitamin D Supplementation Added to Iron Therapy in Children With Iron Deficiency Anemia

This randomized controlled trial will evaluate the effect of two vitamin D3 supplementation regimens, administered in addition to oral iron therapy, on hematological and iron status in children aged 6-60 months with confirmed iron deficiency anemia and vitamin D deficiency. Eligible participants will be randomly assigned in a 1:1 ratio to receive oral elemental iron at 3 mg/kg/day plus either vitamin D3 2000 IU/day or vitamin D3 400 IU/day for 12 weeks. The primary outcome will be the between-group difference in mean change in hemoglobin concentration from baseline to Week 12. Secondary outcomes will include changes in serum ferritin, serum 25-hydroxyvitamin D, red blood cell indices, serum iron, total iron-binding capacity, high-sensitivity C-reactive protein, and exploratory serum hepcidin, as well as adherence and adverse events. Participants will receive follow-up assessments at Weeks 2, 4, 8, and 12 to assess adherence, tolerability, adverse events, and concomitant treatments. Laboratory assessments are planned at baseline and Week 12.

Inclusion Criteria: * Inclusion Criteria: 1. Children aged 6-60 months. 2. Confirmed iron deficiency anemia based on prespecified hemoglobin and iron-status criteria. 3. Vitamin D deficiency defined as serum 25-hydroxyvitamin D \[25(OH)D\] below 20 ng/mL. 4. Written informed consent provided by a parent or legal guardian. Exclusion Criteria: * Exclusion Criteria: 1. Known chronic disease, malabsorption syndrome, or congenital anemia. 2. Severe acute malnutrition, defined in the proposal as WAZ below -3 z-scores. 3. Current or recent iron or vitamin D supplementation within the preceding 3 months. 4. Acute febrile illness or active infection at screening.