Vitamin D3 — Supplements
Secosteroid hormone precursor critical for calcium homeostasis, immune modulation, and musculoskeletal health.
Overview
Vitamin D3 (cholecalciferol) is a secosteroid prohormone synthesized in skin upon UVB exposure and converted to 25-hydroxyvitamin D (calcidiol) in the liver and then to active 1,25-dihydroxyvitamin D (calcitriol) in the kidneys. Vitamin D receptors (VDR) are expressed in virtually all human cells, influencing >1,000 genes. Vitamin D deficiency (<20 ng/mL) affects an estimated 1 billion people worldwide. Strong evidence supports supplementation for bone health, fall prevention, immune function, and reduced all-cause mortality. The Endocrine Society recommends maintaining 25(OH)D levels of 40-60 ng/mL.
Indications
- Vitamin D deficiency and insufficiency
- Bone health and osteoporosis prevention
- Immune system modulation
- Muscle function and fall prevention
- Mood and cognitive support
Mechanism of Action
Cholecalciferol is hydroxylated to 25(OH)D (calcidiol) in the liver by CYP2R1
Dosing
| Compound | Dose | Frequency | Notes |
|---|---|---|---|
| Vitamin D3 (Cholecalciferol) | 5,000 IU | Once daily with fat-containing meal | Adjust based on 25(OH)D levels; target 40-60 ng/mL |
Safety & Contraindications
- Toxicity rare but possible at sustained doses >10,000 IU/day (hypercalcemia, nephrocalcinosis)
- Always co-supplement with K2 to direct calcium to bones rather than vasculature
- Monitor 25(OH)D levels to guide dosing; target 40-60 ng/mL
- Granulomatous diseases (sarcoidosis) may cause hypercalcemia with even moderate D3 doses