Vitamin D3 (Cholecalciferol)
Plain-language research summary.
Detail
immunitybonemoodwomens-health
Hormone-like vitamin that regulates calcium absorption, bone health, muscle function, and immune signaling — especially important for women across pregnancy and menopause.
Common Dietary Sources
- Sunlight (UVB exposure; latitude/season dependent)
- Fatty fish (salmon, sardines), cod liver oil
- Fortified dairy and plant milks
How the Body Uses It
Vitamin D3 is converted in the liver to 25(OH)D, then in the kidneys and immune cells to the active hormone calcitriol. It regulates calcium and phosphorus absorption, supports bone mineralization with calcium and K2, and modulates innate/adaptive immune function.
Supplement Origins
Supplemental D3 is most often derived from lanolin (sheep’s wool); vegan sources use lichen-derived cholecalciferol.
Possible Uses
- Correcting low 25(OH)D levels to support bone density and muscle function
- Immune health support during low-sunlight months
- Perinatal support (with clinician guidance) and post-menopausal bone health
Long-Term Use
Long-term use is common and generally safe within individualized dosing; monitor 25(OH)D levels and balance with Vitamin K2, calcium, and magnesium.
Dose Guidance
Studied
1000–4000 IU/day for maintenance; individualized higher repletion protocols under medical supervision
Take with meals containing fat to enhance absorption. Periodic blood testing of 25(OH)D recommended to target ~30–50 ng/mL (individualized).
Forms
Cholecalciferol (D3)
Standardization: Most bioactive form; lanolin- or lichen-derived
D3 + K2 combination
Standardization: Pairs D3 with MK-7 K2 for calcium utilization
Delivery
Coming soon.
Evidence & Studies
Modest reduction in acute respiratory infection risk in those deficient at baseline
References
Safety & Cautions
Cautions
- Excessive dosing may cause hypercalcemia and kidney strain
- Monitor levels with long-term use or higher doses
Contraindications
- Hypercalcemia or granulomatous diseases (use only with medical guidance)
Interactions
- Works synergistically with Vitamin K2 and calcium for bone health
- May interact with certain steroids and thiazide diuretics (monitor calcium)