What over‑the‑counter vitamin D3 (cholecalciferol) supplement and daily dose should be used for maintenance after an adult with severe vitamin D deficiency (25‑hydroxyvitamin D ≈14 ng/mL) completes a loading regimen of 50,000 IU weekly for 8–12 weeks?

Maintenance Vitamin D3 Supplementation After Loading Dose

Recommended Over-the-Counter Maintenance Regimen

After completing 50,000 IU weekly for 8–12 weeks, transition to cholecalciferol (vitamin D3) 1,500–2,000 IU daily as your maintenance dose. 1, 2, 3

This daily maintenance dose is specifically recommended by bariatric surgery and vitamin D deficiency treatment guidelines to sustain serum 25-hydroxyvitamin D levels ≥30 ng/mL after correction of severe deficiency. 1, 2, 3

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Why Cholecalciferol (Vitamin D3) Over Ergocalciferol (Vitamin D2)

• Cholecalciferol (D3) is strongly preferred over ergocalciferol (D2) because it maintains serum 25(OH)D concentrations for longer periods and has superior bioavailability, particularly when using intermittent dosing schedules. 2, 3
• D3 is the form found in most over-the-counter supplements and is more effective at sustaining levels between doses. 2, 3

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Alternative Maintenance Dosing Options

Daily Dosing (Preferred)

• 1,500–2,000 IU daily is the standard maintenance regimen after loading. 1, 2, 3
• Daily dosing is physiologically preferable and more closely mimics natural vitamin D metabolism. 2, 4

Monthly Dosing (Acceptable Alternative)

• 50,000 IU once monthly (equivalent to approximately 1,600 IU daily) is an acceptable alternative for patients who prefer less frequent dosing. 1, 2, 3
• This regimen maintains adequate levels without excessive accumulation. 2, 3

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Target Serum Level and Monitoring

• Target serum 25(OH)D level: ≥30 ng/mL for optimal bone health, fracture prevention, and fall reduction. 2, 3, 4
• Recheck serum 25(OH)D 3 months after starting maintenance therapy to confirm adequate dosing and adjust if levels remain <30 ng/mL. 2, 3, 4
• If levels remain insufficient despite compliance, increase the maintenance dose by 1,000–2,000 IU daily (or add an additional 50,000 IU monthly dose). 2, 3

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Essential Co-Interventions

• Ensure adequate calcium intake of 1,000–1,500 mg daily from diet plus supplements if needed, as vitamin D enhances calcium absorption and adequate calcium is necessary for optimal bone health. 1, 2, 3
• Calcium supplements should be taken in divided doses of no more than 600 mg at once for optimal absorption. 2, 3

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Dose Adjustment Based on Individual Factors

Higher Maintenance Doses May Be Required For:

• Obesity (BMI ≥30): Vitamin D is sequestered in adipose tissue, requiring 2–4 times higher doses to achieve the same serum levels. 2, 3, 4
• Malabsorption syndromes (inflammatory bowel disease, celiac disease, pancreatic insufficiency): May require 3,000–6,000 IU daily or intramuscular administration if oral supplementation fails. 2, 3, 4
• Post-bariatric surgery patients: Require at least 2,000 IU daily, and often 3,000–6,000 IU daily after malabsorptive procedures. 1, 2, 3
• Chronic kidney disease (stages 3–4): Use standard nutritional vitamin D (cholecalciferol), not active analogs, with the same maintenance doses. 2, 3, 4
• Elderly patients (≥65 years): A minimum of 800 IU daily is recommended, though 1,000–2,000 IU daily more effectively reduces fall and fracture risk. 2, 3, 4
• Dark skin pigmentation: Requires higher doses due to reduced cutaneous synthesis; consider 800–2,000 IU daily. 2, 3, 4

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Safety Parameters

• 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. 2, 3, 4
• The upper safety limit for serum 25(OH)D is 100 ng/mL; toxicity typically occurs only with daily intake exceeding 100,000 IU or serum levels >100 ng/mL. 2, 3, 4
• Monitor serum calcium every 3 months during high-dose therapy to detect hypercalcemia early. 2, 3
• Discontinue all vitamin D immediately if serum calcium exceeds 10.2 mg/dL (2.54 mmol/L). 2, 3

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Critical Pitfalls to Avoid

• Do not use active vitamin D analogs (calcitriol, alfacalcidol, doxercalciferol, paricalcitol) for nutritional vitamin D deficiency, as they bypass normal regulatory mechanisms and dramatically increase hypercalcemia risk. 2, 3, 4
• Avoid single annual mega-doses (≥300,000–500,000 IU), as they have been associated with increased falls, fractures, and adverse outcomes in clinical trials. 2, 3, 4
• Do not assume 800 IU daily is sufficient for all patients—this dose meets the needs of 97.5% of the general population but is inadequate for those with severe deficiency, obesity, malabsorption, or other risk factors. 2, 3, 4
• Do not restart vitamin D supplementation after toxicity until serum 25(OH)D falls below 100 ng/mL and serum calcium remains normal for at least 4 weeks. 2, 3

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Practical Over-the-Counter Product Selection

• Look for cholecalciferol (vitamin D3) supplements in 1,000 IU, 2,000 IU, or 5,000 IU capsules/tablets. 2, 3, 4
• For 1,500–2,000 IU daily: Take one 2,000 IU capsule daily, or one 1,000 IU capsule twice daily. 2, 3
• For 50,000 IU monthly: Some pharmacies carry over-the-counter 50,000 IU cholecalciferol capsules; alternatively, take ten 5,000 IU capsules once monthly. 2, 3
• Vitamin D is fat-soluble: Take with the largest, fattiest meal of the day to maximize absorption. 1

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Expected Outcomes

• A maintenance dose of 1,500–2,000 IU daily typically maintains serum 25(OH)D levels in the 30–50 ng/mL range after successful loading. 2, 3, 5
• As a rule of thumb, 1,000 IU daily increases serum 25(OH)D by approximately 10 ng/mL, though individual responses vary due to genetic factors, body composition, and environmental influences. 2, 3, 4
• Anti-fracture efficacy requires achieved levels ≥30 ng/mL, while anti-fall efficacy begins at ≥24 ng/mL. 2, 3