Standard Dosing for Vitamin D Replacement
Initial Loading Phase for Deficiency (<20 ng/mL)
For adults with documented vitamin D deficiency, initiate treatment with 50,000 IU of vitamin D2 (ergocalciferol) or D3 (cholecalciferol) once weekly for 8-12 weeks. 1
Vitamin D3 (cholecalciferol) is strongly preferred over D2 (ergocalciferol) because it maintains serum levels longer and has superior bioavailability, particularly when using intermittent dosing regimens. 1, 2
For severe deficiency (<10-12 ng/mL), continue the 50,000 IU weekly regimen for the full 12 weeks rather than 8 weeks. 1
This loading dose approach is necessary because standard daily doses would take many weeks to normalize low vitamin D levels. 3
Each 1,000 IU of vitamin D supplementation typically increases serum 25(OH)D levels by approximately 10 ng/mL, though individual responses vary significantly. 1, 2
Maintenance Phase After Loading
After completing the loading dose regimen, transition to maintenance therapy with 800-2,000 IU daily. 1
The minimum maintenance dose is 800 IU daily for most adults, which meets the needs of 97.5% of the population. 2
For optimal health benefits and fracture prevention, 2,000 IU daily is recommended as the preferred maintenance dose after achieving target levels of at least 30 ng/mL. 3, 4
Alternative maintenance regimens include 50,000 IU monthly (equivalent to approximately 1,600 IU daily) for patients who prefer less frequent dosing. 1, 3
Higher Doses for At-Risk Populations
Patients with malabsorption, obesity, or chronic kidney disease require higher maintenance doses of 2,000-4,000 IU daily. 1, 2
Post-bariatric surgery patients need at least 2,000-3,000 IU daily due to reduced absorption. 2
For patients with documented malabsorption syndromes who fail oral supplementation, intramuscular vitamin D3 50,000 IU is the preferred route, resulting in significantly higher 25(OH)D levels compared to oral administration. 3
Obese patients may require 3,000-6,000 IU daily for maintenance due to sequestration in adipose tissue. 2
Target Levels and Monitoring
The target 25(OH)D level should be at least 30 ng/mL (75 nmol/L) for optimal health benefits, particularly for anti-fracture efficacy. 1, 3
Measure 25(OH)D levels after at least 3 months of supplementation to allow serum levels to reach plateau. 1, 2
If using intermittent dosing (weekly or monthly), measure levels just prior to the next scheduled dose. 3
The upper safety limit for 25(OH)D is 100 ng/mL (250 nmol/L). 1, 2
Special Populations Without Baseline Testing
For elderly patients (≥65 years), institutionalized individuals, and those with dark skin or limited sun exposure, supplementation with 800 IU daily can be initiated without baseline testing. 1, 2
- This approach is appropriate for high-risk populations where deficiency is highly likely. 2
Essential Co-Interventions
Ensure adequate calcium intake of 1,000-1,500 mg daily from diet plus supplements if needed. 1, 3
Calcium supplements should be taken in divided doses of no more than 600 mg at once for optimal absorption. 3
Vitamin D enhances calcium absorption, and adequate dietary calcium is necessary for clinical response. 1
Critical Pitfalls to Avoid
Do not use single annual mega-doses (≥500,000 IU) as they have been associated with adverse outcomes including increased falls and fractures. 1, 2
Avoid single very large doses (>300,000 IU) as they may be inefficient or potentially harmful. 1, 3
Never use active vitamin D analogs (calcitriol, alfacalcidol, doxercalciferol, paricalcitol) to treat nutritional vitamin D deficiency, as they bypass normal regulatory mechanisms and carry higher risk of hypercalcemia. 3
Daily or weekly dosing is physiologically preferable to monthly bolus doses for routine supplementation. 1
Safety Considerations
Daily doses up to 4,000 IU are generally considered safe for adults, with vitamin D toxicity being rare. 2, 3