What is the appropriate weekly vitamin D3 dose for an otherwise healthy 11‑year‑old with a serum 25‑hydroxyvitamin D level of 17 ng/mL?

Vitamin D3 Weekly Dosing for an 11-Year-Old with Deficiency

For an 11-year-old with a serum 25-hydroxyvitamin D level of 17 ng/mL (deficiency), administer 50,000 IU of vitamin D3 once weekly for 8–12 weeks, followed by maintenance therapy of 1,000–2,000 IU daily. 1

Initial Loading Phase

• Start with 50,000 IU of vitamin D3 (cholecalciferol) once weekly for 8–12 weeks to rapidly correct the deficiency, as this is the standard evidence-based loading regimen for pediatric and adolescent populations with documented deficiency. 1, 2, 3

• Vitamin D3 is strongly preferred over vitamin D2 (ergocalciferol) because it maintains serum levels longer and has superior bioavailability, particularly important for intermittent (weekly) dosing schedules. 1, 4

• A level of 17 ng/mL represents moderate deficiency (below the 20 ng/mL threshold), warranting an 8-week loading course; if the level were below 10 ng/mL (severe deficiency), extend the loading phase to 12 weeks. 1

• The 50,000 IU weekly regimen has been validated in adolescents aged 13 ± 2 years and shown to safely and effectively raise 25(OH)D levels to the target range without adverse events. 2, 3

Maintenance Phase After Loading

• Transition to 1,000–2,000 IU of vitamin D3 daily after completing the 8-week loading phase to maintain optimal levels and prevent recurrence. 1, 5, 4

• For adolescents, a daily maintenance dose of 2,000 IU has been shown to raise 25(OH)D ≥20 ng/mL in 96% of subjects and ≥30 ng/mL in 64%, making it highly effective for this age group. 6

• An alternative maintenance regimen is 50,000 IU once monthly (equivalent to approximately 1,600 IU daily), which can improve adherence if daily dosing is challenging. 1, 2

Target Serum Levels and Monitoring

• The target serum 25(OH)D level is ≥30 ng/mL for optimal bone health, fracture prevention, and overall health benefits in growing adolescents. 1, 5, 4

• Recheck serum 25(OH)D levels 3 months after starting supplementation (i.e., after completing the loading phase and initiating maintenance) to confirm adequate response and adjust dosing if needed. 1, 5, 4

• If using weekly dosing, measure the level just prior to the next scheduled dose to accurately reflect trough concentrations. 1

• The upper safety limit for serum 25(OH)D is 100 ng/mL; toxicity is extremely rare in pediatric populations with standard dosing regimens. 1, 5

Essential Co-Interventions

• Ensure adequate calcium intake of 1,000–1,200 mg daily from diet plus supplements if needed, as vitamin D works synergistically with calcium for bone mineralization during adolescent growth. 1, 4, 3

• Calcium supplements should be taken in divided doses of no more than 600 mg at once for optimal absorption. 1, 4

• Administer vitamin D with the largest, fattiest meal of the day to maximize absorption, as it is a fat-soluble vitamin. 1

Special Considerations for Pediatric Populations

• Adherence is typically 100% with weekly dosing in adolescents, making it a practical and effective regimen for this age group. 2

• For children with malabsorption syndromes (e.g., inflammatory bowel disease, celiac disease, cystic fibrosis), consider higher oral doses (4,000–5,000 IU daily) or intramuscular administration if oral supplementation fails. 1, 5

• Obese adolescents may require higher maintenance doses (up to 3,000–6,000 IU daily) due to sequestration of vitamin D in adipose tissue. 5

Critical Pitfalls to Avoid

• Do not use active vitamin D analogs (calcitriol, alfacalcidol) to treat nutritional vitamin D deficiency, as they bypass normal regulatory mechanisms and increase hypercalcemia risk. 1, 4

• Avoid single ultra-high loading doses (>300,000 IU) or annual mega-doses (≥500,000 IU), as they have been associated with adverse outcomes including increased falls and fractures, and are inefficient compared to weekly or daily dosing. 1, 5

• Do not rely on 400 IU daily as initial treatment for documented deficiency, as this dose is insufficient to correct deficiency in a reasonable timeframe and will result in persistent low levels. 7, 6

• Do not use sun exposure as a primary strategy for vitamin D repletion due to increased skin cancer risk and unreliable synthesis, especially in darker-skinned individuals. 5

Evidence-Based Dosing Algorithm

1. Confirm deficiency: Serum 25(OH)D = 17 ng/mL (below 20 ng/mL threshold) 1
2. Loading phase: 50,000 IU vitamin D3 once weekly × 8 weeks 1, 2, 3
3. Maintenance phase: 1,000–2,000 IU vitamin D3 daily (or 50,000 IU monthly) 1, 5, 6
4. Calcium co-supplementation: 1,000–1,200 mg daily in divided doses 1, 4, 3
5. Monitoring: Recheck 25(OH)D at 3 months, target ≥30 ng/mL 1, 5, 4
6. Long-term: Continue maintenance dosing and recheck annually once stable 1, 5

Expected Outcomes

• The 50,000 IU weekly regimen typically raises 25(OH)D by approximately 40–70 ng/mL (16–28 ng/mL) over 8–12 weeks, which should bring the level from 17 ng/mL to at least 33–45 ng/mL if the patient is responding normally. 1

• Using the rule of thumb that 1,000 IU daily increases serum 25(OH)D by approximately 10 ng/mL, a maintenance dose of 2,000 IU daily should sustain levels in the optimal 30–50 ng/mL range. 1, 5

• Adherence with weekly dosing is excellent in adolescents, and adverse events are minor and rare with standard regimens. 2, 3