What is the recommended maintenance dose of vitamin D3 (cholecalciferol) after 6 weeks of supplementation?

Maintenance Vitamin D3 Dosing After 6-Week Loading Phase

After completing a 6-week loading regimen of vitamin D3, transition to a maintenance dose of at least 2,000 IU daily to sustain optimal 25(OH)D levels above 30 ng/mL. 1

Understanding the Maintenance Phase

After correcting vitamin D deficiency with a loading dose protocol (typically 50,000 IU weekly for 6-8 weeks), the goal shifts to maintaining serum 25(OH)D levels at or above 30 ng/mL for optimal anti-fracture efficacy. 1

Standard Maintenance Dosing Options

Daily regimen:

• 2,000 IU daily is the minimum effective maintenance dose for most adults after loading. 1
• For elderly patients (≥65 years), 800-1,000 IU daily may be sufficient, though higher doses of 700-1,000 IU daily provide better fall and fracture risk reduction. 1

Intermittent regimen:

• 50,000 IU monthly (equivalent to approximately 1,600 IU daily) can maintain adequate levels. 1
• This option improves compliance for patients who prefer less frequent dosing. 1

Critical Evidence on Maintenance Dosing

The 2,000 IU daily dose may be insufficient for many patients. A prospective study found that after achieving adequate levels with 50,000 IU weekly for 3 months, patients given 2,000 IU daily for maintenance saw their 25(OH)D levels drop from 36.97 ng/mL to 20.38 ng/mL—falling below the optimal 30 ng/mL target. 2

Higher maintenance doses should be considered for:

• Obese patients (BMI >30): May require 3,000-6,000 IU daily. 3
• Patients with malabsorption syndromes: May need 4,000-5,000 IU daily or intramuscular administration. 1
• Post-bariatric surgery patients: Require at least 2,000-3,000 IU daily. 1, 3
• Patients on medications affecting vitamin D metabolism: Consider 7,000 IU daily or 30,000 IU weekly. 4

Vitamin D3 vs D2 for Maintenance

Cholecalciferol (D3) is strongly preferred over ergocalciferol (D2) for maintenance therapy because D3 maintains serum 25(OH)D concentrations for longer periods, particularly with intermittent dosing schedules. 5, 1

Monitoring Protocol

Recheck 25(OH)D levels 3 months after starting maintenance therapy to confirm adequate dosing. 5, 1

• If using intermittent dosing (monthly), measure levels just prior to the next scheduled dose. 1
• Target level: ≥30 ng/mL for anti-fracture efficacy. 1
• Upper safety limit: 100 ng/mL. 1
• If levels remain below 30 ng/mL, increase the maintenance dose. 5

Essential Co-Interventions

Ensure adequate calcium intake of 1,000-1,500 mg daily from diet plus supplements if needed to support bone health. 1

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

Common Pitfalls to Avoid

Do not assume 800 IU daily is sufficient for all patients. While this dose meets population-level recommendations for adults over 70 years 3, individual requirements vary significantly based on:

• Baseline vitamin D status (lower baseline = better response to supplementation). 6
• Body weight and adiposity (obese patients sequester vitamin D in adipose tissue). 3, 4
• Genetic variations in vitamin D metabolism. 1
• Presence of malabsorption conditions. 1

Avoid single ultra-high loading doses (>300,000 IU at once) as they have been associated with increased fall and fracture risk. 1

Do not use active vitamin D analogs (calcitriol, alfacalcidol) for nutritional vitamin D deficiency maintenance. These are reserved for specific conditions like advanced chronic kidney disease. 1

Practical Dosing Algorithm

1. Standard risk patients: Start with 2,000 IU daily or 50,000 IU monthly. 1
2. High-risk patients (obesity, malabsorption, elderly with falls): Start with 3,000-4,000 IU daily or 30,000 IU weekly. 1, 4
3. Recheck levels at 3 months. 1
4. If 25(OH)D <30 ng/mL: Increase dose by 1,000-2,000 IU daily (or equivalent intermittent dose). 5
5. If 25(OH)D 30-50 ng/mL: Continue current dose. 1
6. If 25(OH)D >100 ng/mL: Reduce or temporarily discontinue supplementation. 1

Safety Considerations

Daily doses up to 4,000 IU are generally safe for adults, with some evidence supporting up to 10,000 IU daily for several months without adverse effects. 1, 3

Vitamin D toxicity (hypercalcemia) is rare and typically occurs only with prolonged intake exceeding 10,000 IU daily or when 25(OH)D levels exceed 100 ng/mL. 1