What is the appropriate vitamin D (cholecalciferol) treatment regimen and dosing for a 9‑year‑old child weighing 30 kg with a 25‑hydroxy‑vitamin D level of 13.8 ng/mL (deficiency)?

Treatment of Vitamin D Deficiency in a 9-Year-Old Child

For this 9-year-old child with severe vitamin D deficiency (13.8 ng/mL), initiate treatment with 2,000 IU of cholecalciferol (vitamin D3) daily for 12 weeks, or alternatively 50,000 IU every other week for 12 weeks. 1

Initial Treatment Phase (Loading Dose)

For a child with a 25(OH)D level of 13.8 ng/mL, this represents severe deficiency requiring aggressive repletion:

• Administer 2,000 IU of vitamin D3 daily for 12 weeks as the preferred regimen 1
• Alternative regimen: 50,000 IU every other week for 12 weeks if adherence to daily dosing is a concern 1, 2
• Cholecalciferol (vitamin D3) is strongly preferred over ergocalciferol (vitamin D2) due to superior bioefficacy and more reliable absorption 1, 2

The goal is to achieve a 25(OH)D level above 20 ng/mL (50 nmol/L), which indicates sufficiency and protects against rickets and metabolic bone disease 1, 2.

Essential Concurrent Calcium Supplementation

Provide 250-500 mg/day of elemental calcium during the entire treatment period to support bone mineralization and prevent hypocalcemia, particularly critical given the severity of deficiency 1. This is not optional—vitamin D improves calcium absorption, and adequate calcium substrate is necessary for proper bone health 1.

Monitoring Strategy

• Recheck 25(OH)D levels after the 12-week treatment period to confirm normalization above 20 ng/mL 1
• Assess for clinical manifestations of rickets at baseline, including bone deformities, leg bowing, or rachitic rosary, as this level of deficiency may already have caused skeletal changes 1
• Consider baseline laboratory evaluation including serum calcium, phosphorus, alkaline phosphatase, and parathyroid hormone to assess for metabolic bone disease 1

Maintenance Phase (After Initial Treatment)

Once 25(OH)D levels normalize:

• Continue with 600 IU of vitamin D3 daily as maintenance therapy for children aged 1-18 years 1, 2
• Monitor 25(OH)D levels every 6-12 months, especially during winter months when sun exposure is limited 1

Safety Considerations

• The upper tolerable limit for a 9-year-old is 4,000 IU/day, so the recommended 2,000 IU daily treatment dose is well within safe parameters 1, 2
• Vitamin D toxicity is rare at recommended doses but can occur with serum concentrations >375 nmol/L (>150 ng/mL), causing hypercalcemia and hyperphosphatemia 1
• Do not use active vitamin D analogs (calcitriol, alfacalcidol) to treat nutritional vitamin D deficiency—these are reserved for specific conditions like chronic kidney disease 1

Critical Pitfalls to Avoid

• Ensure adherence to the full 12-week treatment regimen, as inconsistent supplementation is the most common cause of treatment failure 1, 3
• Do not skip calcium supplementation—vitamin D alone without adequate calcium can lead to suboptimal bone mineralization 1
• Do not assume dietary sources alone will correct severe deficiency—supplementation is mandatory at this level 1
• Assess for underlying causes such as malabsorption (celiac disease, inflammatory bowel disease), limited sun exposure, or dietary insufficiency that may require ongoing higher maintenance doses 1