What is the recommended dosing regimen for vitamin D (Vit D) deficiency in adults?

Vitamin D Dosing for Adults

Treatment Approach Based on Vitamin D Status

For documented vitamin D deficiency (<20 ng/mL), initiate treatment with ergocalciferol 50,000 IU once weekly for 8-12 weeks, followed by maintenance therapy with 800-2,000 IU daily. 1, 2

Initial Loading Phase for Deficiency

• Standard deficiency (<20 ng/mL): Prescribe 50,000 IU of vitamin D2 (ergocalciferol) or D3 (cholecalciferol) once weekly for 8-12 weeks 1, 2
• Severe deficiency (<10-12 ng/mL): Use the same 50,000 IU weekly regimen for 12 weeks, particularly if symptomatic or at high fracture risk 1
• Vitamin D3 (cholecalciferol) is preferred over D2 (ergocalciferol) for maintenance therapy, especially with intermittent dosing, as it maintains serum levels longer 1, 2

Maintenance Therapy After Correction

• Standard maintenance: Transition to 800-2,000 IU daily after completing the loading phase 1, 2
• Alternative intermittent dosing: 50,000 IU monthly (equivalent to approximately 1,600 IU daily) is acceptable for patients preferring less frequent dosing 1, 2
• The Endocrine Society recommends at least 2,000 IU daily for optimal health benefits after deficiency correction 1

Maintenance Dosing for Prevention (Without Documented Deficiency)

• Adults aged 19-70 years: 600-800 IU daily 3
• Adults >70 years: 800 IU daily minimum 1, 3
• Elderly patients ≥65 years: 800-1,000 IU daily to reduce fall and fracture risk 1
• At-risk populations (dark-skinned, veiled, institutionalized, limited sun exposure): 800 IU daily without baseline testing 1, 3

Higher Doses for Special Populations

• Malabsorption syndromes (post-bariatric surgery, inflammatory bowel disease, celiac disease): 2,000-6,000 IU daily maintenance, or consider intramuscular administration 1, 3
• Obesity: Higher doses (2,000-4,000 IU daily) may be required due to sequestration in adipose tissue 3, 2
• Chronic kidney disease (GFR 20-60 mL/min/1.73m²): Treat with ergocalciferol or cholecalciferol using standard deficiency protocols 1

Monitoring Protocol

• Initial follow-up: Measure 25(OH)D levels 3-6 months after starting supplementation to assess response 1, 2
• Target level: Aim for serum 25(OH)D ≥30 ng/mL for optimal health benefits, particularly for anti-fracture efficacy 1, 2
• Upper safety limit: 100 ng/mL; levels above this increase toxicity risk 1, 3
• For intermittent dosing regimens (weekly/monthly), measure levels just prior to the next scheduled dose 1

Practical Dosing Considerations

• Rule of thumb: Each 1,000 IU daily increases serum 25(OH)D by approximately 10 ng/mL, though individual responses vary significantly 1, 3, 2
• Daily dosing is physiologically preferred, but weekly or monthly regimens achieve similar 25(OH)D concentrations 1, 3
• Ensure adequate calcium intake of 1,000-1,500 mg daily (diet plus supplements) alongside vitamin D 1, 2

Critical Safety Considerations

• Safe upper limit: Daily doses up to 4,000 IU are generally safe for adults 1, 3
• Avoid mega-doses: Single doses >300,000-500,000 IU should be avoided as they may be inefficient or harmful, particularly for fall and fracture prevention 1, 3
• Toxicity risk: Prolonged daily doses >10,000 IU can cause hypercalcemia, hypercalciuria, and renal complications 1
• Vitamin D supplementation benefits are primarily seen in those with documented deficiency, not in the general population with normal levels 1, 2

Common Pitfalls to Avoid

• Do not use active vitamin D analogs (calcitriol, alfacalcidol, doxercalciferol, paricalcitol) to treat nutritional vitamin D deficiency 1
• Individual response to supplementation varies significantly due to genetic differences in vitamin D metabolism, making monitoring essential 1
• Inflammation (CRP >40 mg/L) can significantly reduce plasma vitamin D levels, complicating interpretation 1
• For patients with malabsorption not responding to oral supplementation, consider intramuscular vitamin D 50,000 IU (though availability varies by country) 1