What is the best form of vitamin d?
3 forms compared by what actually reaches your bloodstream. Absorption ranges from 60% to 95% — a difference that matters more than the milligrams on the label.
Ranked by absorption
Higher means more of the dose reaches youShort answer
Vitamin D3 (Calcidiol) absorbs best — 95%.
Fast-acting vitamin D therapy. Typical dose 5-20 mcg (medical supervision), about $80 a month. The cheapest option is Vitamin D3 at $8, but its absorption score is only 85 of 100.
Which form for which goal
Best absorbed option that covers each useSame compound, different carrier — the goal changes which trade-off matters, not what the mineral does.
Every form side by side
| Form | Absorbed | Elemental | Cost / 100 mcg delivered | Per month | Dose |
|---|---|---|---|---|---|
| Vitamin D3 (Calcidiol) | 95% | — | $22.46 | $80 | 5-20 mcg (medical supervision) |
| Vitamin D3 | 85% | — | — | $8 | 1000-2000 IU |
| Vitamin D2 (Ergocalciferol) | 60% | — | — | $15 | 2000-4000 IU |
What not to take with vitamin d
Same rules for every form — the interaction belongs to the mineral, not the carrierSeparating the two by two to four hours removes most of these: they compete for the same transporters in the gut, not in the bloodstream. Splitting the day is what solves a conflict — dropping one of the two is rarely necessary.
Medication interactions
Increased risk of hypercalcemia · Avoid combination or monitor calcium closely
Hypercalcemia increases digoxin toxicity risk · Monitor calcium and digoxin levels closely
May reduce effectiveness · Monitor blood pressure response
Reduces vitamin D effectiveness · Increase vitamin D dose by 2-3x
Increases vitamin D metabolism · Monitor vitamin D status
Prescription medicine is your doctor's call, not ours — this is what the records list.
How much is too much
Upper limit for adults: 100 mcg (4000 IU) a day, per NIH ODS.
Signs of overshooting it: hypercalcemia (high blood calcium), nausea, vomiting, and weakness, kidney stones and damage, heart rhythm abnormalities.
276 reports to the FDA name vitamin-d as the suspect product.
Most reported: choking (76), dysphagia (38), dyspnoea (25), foreign body trauma (22). Serious outcomes: 88% of them.
Counted from FDA CAERS by parsing each report's product list, not by keyword — a report where the product was merely present does not count.
Head to head
How to read this
- Absorption is the share of the dose that reaches your bloodstream — the number that decides whether the milligrams on the label mean anything.
- A cheaper form at half the absorption is not cheaper per unit delivered.
- Safety here reflects tolerance at normal doses, not toxicity risk.
- Evidence A means the form itself was studied, not just the parent compound.
Compiled by Denis, who maintains this database and holds no medical qualification. Absorption figures and cost-per-absorbed values are derived by published formulas from cited sources — see the arithmetic.
Common questions
What is the best form of vitamin d?
Vitamin D3 (Calcidiol) — it scores 95 of 100 on absorption, the highest of the 3 forms here. Fast-acting vitamin D therapy. Typical dose 5-20 mcg (medical supervision).
Which form of vitamin d is worst absorbed?
Vitamin D2 (Ergocalciferol) at 60%. It is usually the cheapest option, which is exactly why it ends up in budget products.
Is the expensive form of vitamin d worth it?
Compare per unit delivered, not per bottle. Vitamin D3 costs $8 a month at 85% absorption, Vitamin D3 (Calcidiol) costs $80 at 95%.
How much vitamin d should you take?
Doses differ by form: Vitamin D3 (Calcidiol) 5-20 mcg (medical supervision); Vitamin D3 1000-2000 IU; Vitamin D2 (Ergocalciferol) 2000-4000 IU.