Vitamin D3
Cholecalciferol · Vitamin D
Cholecalciferol; fat-soluble vitamin important for bone health, immunity, and hormonal balance.
Key takeaways
- Fat-soluble vitamin converted to the hormone calcitriol; central to calcium and bone health.
- Correcting true deficiency is well supported; benefits in replete people are unproven.
- VITAL (n=25,871) found no cancer or cardiovascular benefit at 2000 IU daily.
- Half-life runs weeks via fat storage; dose by serum 25(OH)D, not by feel.
Overview
What it is
Vitamin D3 (cholecalciferol) is a fat-soluble vitamin the body converts to calcifediol and then the active hormone calcitriol, which regulates calcium absorption, bone mineralization, and immune signaling. It comes from sun exposure, diet, and supplements, and the standard clinical route is oral.
Pharmacokinetics
The circulating marker 25-hydroxyvitamin D has a half-life of roughly two to three weeks, and the parent compound lingers in fat tissue even longer, so levels change slowly and dosing is guided by lab values rather than daily kinetics. It's excluded from the plotter for that reason.
What the evidence says
Strong for correcting deficiency and protecting bone in deficient people. For everyone else the big trials disappoint: VITAL, a randomized trial of nearly 26,000 adults, found no reduction in cancer or cardiovascular events at 2000 IU daily. Toxicity (hypercalcemia) is real at excessive doses.
Reported dosing protocols
Protocols reported in research literature and clinic/community use — informational context, not a dosing recommendation.
| Use case | Dose | Route | Frequency | Duration |
|---|---|---|---|---|
| General repletion (reported clinical) | 1000–2000 IU (25–50 mcg) | Oral | Once daily | Ongoing; recheck 25(OH)D in 2–3 months |
| Deficiency treatment (prescription) | 50,000 IU | Oral | Once weekly | 6–8 weeks, then maintenance |
About this entry
This catalog entry is informational only. It is not a single-agent peptide with a modelled pharmacokinetic curve, so it cannot be opened in the plotter.
Frequently asked questions
How much vitamin D is too much?
The tolerable upper intake for adults is commonly set at 4000 IU (100 mcg) daily. Chronic intake far above that can cause hypercalcemia (nausea, kidney stones, confusion), which is why high-dose use belongs under lab monitoring.
Does vitamin D prevent colds, cancer, or heart disease?
The largest randomized trial, VITAL, found no reduction in cancer or cardiovascular events at 2000 IU daily in generally healthy adults. Respiratory-infection meta-analyses suggest a small benefit mainly in deficient people. Correcting deficiency is the solid use case.
Is injectable vitamin D better than oral?
Rarely needed. Oral cholecalciferol raises 25(OH)D reliably in most people. Injection is reserved for documented malabsorption or severe deficiency under medical care, and it offers no advantage otherwise.
References
- NIH ODS Vitamin D Fact Sheet + StatPearls (Cholecalciferol) — 25(OH)D calcifediol half-life ~15 days; calcitriol ~15 hours. Parent D3 tissue storage ~50 days.
- NIH Office of Dietary Supplements — Vitamin D fact sheet — Intake ranges, upper limits, and evidence summary.
- StatPearls — Cholecalciferol — Clinical pharmacology, dosing, and toxicity reference.
- Manson et al., NEJM 2019 — VITAL trial — n=25,871; 2000 IU/day showed no reduction in invasive cancer or major cardiovascular events.
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