Vitamin D Deficiency Repletion and Maintenance Guidelines

Definition and Target Serum Levels

Vitamin D deficiency is defined as a serum 25‑hydroxyvitamin D concentration < 20 ng/mL, while optimal sufficiency is achieved at ≥ 30 ng/mL. 1

For individuals with a 25‑hydroxyvitamin D level around 15 ng/mL, a high‑dose regimen of ergocalciferol (vitamin D₂) 50,000 IU once weekly for 8 weeks is recommended to reach a target ≥ 30 ng/mL. 1, 4, 3
An alternative loading strategy uses cholecalciferol (vitamin D₃) 4,000–6,000 IU daily for 8–12 weeks. 5, 6
Each additional 1,000 IU of daily vitamin D intake typically raises serum 25‑hydroxyvitamin D by ≈10 ng/mL; therefore, the 50,000 IU weekly regimen (≈7,000 IU daily) is expected to increase the level from 15 ng/mL to >30 ng/mL over the 8‑week period. 1, 4

If the post‑loading serum level is ≥ 30 ng/mL, continue with vitamin D₃ 800–2,000 IU daily (or an equivalent dose of vitamin D₂). 1, 4, 7
If the level remains < 30 ng/mL, maintain a higher‑dose supplementation regimen and re‑measure serum 25‑hydroxyvitamin D in 3 months. 2, 3

Vitamin D₃ (cholecalciferol) is preferred for maintenance because it sustains serum concentrations more effectively with intermittent dosing, although daily dosing of vitamin D₂ yields comparable results. 4, 7

Re‑check serum 25‑hydroxyvitamin D 3 months after completing the loading phase (or before the next intermittent dose if using a monthly schedule). 7
Monitor serum calcium during high‑dose therapy; hypercalcemia is rare at the recommended dosing levels. 1, 3
Once vitamin D repletion is achieved, annual monitoring of serum 25‑hydroxyvitamin D is reasonable while continuing supplementation. 8

Very high intermittent dosing (e.g., 500,000 IU annually) is associated with increased falls and fractures and should be avoided; weekly or monthly dosing regimens are safer. 4, 7
Toxicity generally occurs only with daily doses > 50,000 IU, leading to serum 25‑hydroxyvitamin D > 150 ng/mL; the upper safety limit is 100 ng/mL, with a clinical target range of 30–50 ng/mL. 2, 3, 1, 4
Adequate calcium intake (approximately 1,000 mg daily for this age group) should be ensured to support bone health during vitamin D repletion. 2, 3