Vitamin D Dosage Guide
Recommended and upper-limit intakes of cholecalciferol (vitamin D3) by age, plus repletion protocols indexed to baseline serum 25-hydroxyvitamin D — pulled from the Institute of Medicine (2011) and Endocrine Society (2011) guidelines.
Daily intake by age (IOM RDA)
| Age group | RDA / AI (IU/day) | UL (IU/day) |
|---|---|---|
| Infants 0–6 months | 400 | 1,000 |
| Infants 7–12 months | 400 | 1,500 |
| Children 1–3 years | 600 | 2,500 |
| Children 4–8 years | 600 | 3,000 |
| Ages 9–70 | 600 | 4,000 |
| Ages 71+ | 800 | 4,000 |
Repletion protocols by baseline 25(OH)D
Below are typical clinical repletion regimens for adults, drawn from the Endocrine Society 2011 clinical practice guideline. These are starting points — actual protocols vary by body weight, comorbidities, and medications.
< 12 ng/mL (severe)
Regimen: 50,000 IU/week × 8 wk → 1,500–2,000 IU/d maintenance
Under physician supervision. Check labs including PTH and calcium.
12–20 ng/mL (deficient)
Regimen: 6,000 IU/d × 8 wk → 1,500–2,000 IU/d maintenance
Recheck 25(OH)D after 3 months.
20–30 ng/mL (insufficient)
Regimen: 1,000–2,000 IU/d
Retest after 3 months; adjust based on response.
30–50 ng/mL (sufficient)
Regimen: 600–1,000 IU/d maintenance
Adjust seasonally; higher in winter if minimal sun exposure.
Cholecalciferol (D3) vs ergocalciferol (D2)
Both raise serum 25(OH)D, but per-mole they differ. Tripkovic et al.'s 2012 meta-analysis found D3 approximately 60–90% more effective than D2 at raising 25(OH)D at equivalent oral doses. In practice, if your prescription reads "ergocalciferol 50,000 IU," ask whether you can substitute cholecalciferol at the same dose for better response.
Unit conversion
IU to µg
40 IU = 1 µg
µg to IU
1 µg = 40 IU
Safety and the upper limit
The Tolerable Upper Intake Level (UL) for adults is 4,000 IU/day from all sources (food + supplements). This is set conservatively; toxicity in observational studies does not appear until serum 25(OH)D exceeds ~150 ng/mL, which typically requires sustained intake of 40,000+ IU/day for months. Sun exposure alone cannot cause toxicity due to the photoequilibrium that degrades previtamin D3 at high UV doses.