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Comparative guide · 5 min read

Vitamin D3 vs D2 — which form should you actually buy?

Updated 2026-05-09 · Reviewed by SupplementScore editors · No sponsorships

They sit side by side on the shelf, both labelled "vitamin D", and they are emphatically not interchangeable. Vitamin D3 (cholecalciferol) is the form your skin makes from sunlight and the form found in animal foods. Vitamin D2 (ergocalciferol) is plant- or fungus-derived. They share a common downstream metabolism, but D3 raises and sustains 25-hydroxyvitamin D — the standard blood marker — more reliably than D2 at equivalent doses. For most buyers, D3 is the default; D2 is a niche choice with one specific advantage.

Quick verdict

GoalBetter choiceWhy
Raising 25(OH)D level efficiently D3 Per-IU, D3 raises and sustains 25(OH)D ~50–80% more than D2 in head-to-head trials. Tier 1, evidence 4/5.
Strict vegan supplementation D2 — or lichen-derived D3 Most D3 is sheep-lanolin-derived. Vegans wanting D3 should look for "lichen-derived" or "vegan D3" — these now exist and outperform D2.
Prescription high-dose for deficiency D2 (often) The 50,000 IU prescription weekly product in the US is typically D2 (Drisdol). Works at the high doses used clinically; cheaper to manufacture at pharmaceutical grade.
Maintenance dosing in deficiency-prone groups D3 Smaller, daily doses with a stable steady-state — closer to the physiological pattern.
Lowest cost per effective dose D3 Bulk D3 is one of the cheapest supplements available; pennies a day at maintenance doses.

How they compare on the things that matter

Mechanism — same target, different efficiency

Both D2 and D3 are precursors. After ingestion, both are hydroxylated in the liver to 25-hydroxyvitamin D (the storage form, what gets measured on labs) and then in the kidney to 1,25-dihydroxyvitamin D (the active hormone). The structural difference is a methyl group on the side chain — small chemically, but enough to change binding affinity to vitamin D-binding protein, half-life in circulation, and rate of conversion to the active metabolite.

The practical consequence: at any given dose, D3 raises 25(OH)D higher and keeps it elevated longer than D2. In Tripkovic 2012 (a meta-analysis of head-to-head trials), D3 was approximately 1.7× more effective at raising 25(OH)D than D2. The Logan 2013 trial in older adults confirmed similar findings at standard doses.

Evidence base

Half-life and dosing pattern

D3 has a longer effective half-life on the storage form (25(OH)D) than D2. This is part of why D3 sustains levels better between doses. Practical implication: D3 is more forgiving of inconsistent daily dosing, and weekly D3 dosing (e.g. 7,000 IU once weekly) maintains 25(OH)D about as well as 1,000 IU daily. D2 used at large weekly doses also works for repletion but tends to peak and trough more.

Practical rule. Default to D3. Only use D2 if you need a strict-vegan option and cannot find a lichen-derived D3, or if your physician has prescribed Drisdol for repletion.

Vegan considerations

Conventional D3 is extracted from sheep wool grease (lanolin). Vegans avoiding all animal-derived inputs have historically had D2 as their only option, which is real but suboptimal. Lichen-derived D3 ("vegan D3") has been on the market for years now, is functionally identical to lanolin-derived D3, and outperforms D2 in head-to-head dose-equivalent trials. The price premium has narrowed considerably — for ethical vegan consumers, lichen D3 is the better-evidenced choice.

What about K2 stacking?

Combination D3 + K2 products are popular on the theory that K2 directs calcium toward bone rather than soft tissue. The mechanistic case is plausible; the clinical-endpoint evidence in healthy people without deficiency or osteoporosis is modest. The combination is reasonable for older adults, those with osteopenia, or anyone supplementing high-dose D3 long-term — but skip the premium if you're paying significantly more than D3 alone plus a separate cheap K2 (MK-7) product.

Safety

Toxicity from either form is rare at doses up to 4,000 IU/day. Hypercalcaemia is the limiting adverse outcome at very high chronic doses (typically >10,000 IU/day for many months without medical supervision). People with sarcoidosis, primary hyperparathyroidism, or granulomatous disease are at increased risk of hypercalcaemia at otherwise standard doses and should not supplement without endocrine supervision. Test 25(OH)D before and after starting if you're targeting a specific level, especially at doses >2,000 IU/day.

What the price difference buys you

Both forms are inexpensive at maintenance doses. A 1-year supply of D3 at 1,000–2,000 IU/day runs about $10–20. D2 in over-the-counter forms is similarly priced; prescription Drisdol (D2 at 50,000 IU weekly) is also low-cost. The economic argument is essentially neutral — the differentiator is biological efficacy, where D3 has the edge.

What we'd actually buy

For most adults: D3 at 1,000–2,000 IU daily, taken with a fat-containing meal (it's lipid-soluble). Adults with documented deficiency (25(OH)D < 20 ng/mL) typically need higher repletion doses for 8–12 weeks before stepping down to maintenance — work with a clinician on this. For vegans: lichen-derived D3 at the same dose ranges. Skip the "10,000 IU mega-dose" products for routine use; they aren't more effective and increase the toxicity risk over years of use.

Sources

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