Vitamin D3 vs D2: Which Raises Blood Levels More

Two molecules, one job

Both forms are inactive precursors. The liver converts either one to 25-hydroxyvitamin D, and the kidneys convert that into the active hormone. Downstream of the first hydroxylation, the pathways converge, and the receptors can't tell the difference.

The difference is upstream, in how much 25-hydroxyvitamin D each form produces and how long it stays.

D3 is made in skin from 7-dehydrocholesterol when UVB hits it. Supplemental D3 comes from lanolin, which is why vegan products use D2 or lichen-derived D3. D2 is produced by irradiating yeast and is the traditional pharmaceutical form.

What the head-to-head data shows

The most cited comparison is a 2012 meta-analysis in the American Journal of Clinical Nutrition that pooled seven randomized trials comparing bolus doses of D2 and D3. It found D3 more effective at raising serum 25-hydroxyvitamin D, and D2 associated with a faster decline once dosing stopped.

The bolus framing matters. Most of those trials used large single doses, and that's the regime where D2 looks worst. Daily smaller doses show a smaller gap, and some daily comparisons found no meaningful difference.

There's also a pharmacokinetic quirk. D2 produces its own metabolite, 25-hydroxyvitamin D2, and standard assays measure both. Early studies that used assays failing to detect D2 metabolites overstated the difference. Modern liquid chromatography assays handle both, which is one reason older papers look more dramatic than newer ones.

The outcomes question

Here's where it gets uncomfortable for anyone who wants a clean answer.

The trials that showed reductions in falls and fractures used both forms. The 2003 BMJ trial that gave 100,000 IU every four months used D3 and reduced fractures. The 2010 JAMA trial that gave 500,000 IU annually used D2 and increased falls. A trial of 300,000 IU intramuscular D2 found no effect on nonvertebral fractures.

Read that again. The positive fracture trial used D3. The negative ones used D2 at enormous single doses. It's tempting to conclude that D2 is the problem, but the annual-dose regime itself is suspect, and the dose routes don't match cleanly. The 2012 commentary in the Journal of Clinical Investigation made the point directly: there's no consistent pattern of one form beating the other on clinical outcomes.

So the two statements stand together. D3 raises the marker more efficiently. The trials haven't shown that this translates into fewer fractures, and confounding by dose regime prevents a confident attribution.

What this means at the counter

For a daily supplement in the 600 to 2,000 IU range, D3 is the reasonable default. It's cheaper, it's the form the largest trials used, and the meta-analytic edge is real even if the clinical consequence is unproven.

D2 isn't a bad product. It's the correct choice for people following a strict vegan diet who want a form that isn't lanolin-derived, and it remains the standard high-dose prescription format for treating documented deficiency.

The fortified food layer adds its own wrinkle. In the United States, milk is voluntarily fortified with vitamin D, and brands use D2, D3, or both. Mushrooms treated with UV light provide D2. Fatty fish provides D3. Someone eating a varied diet gets a mixture without trying.

Dosing equivalence

There is no fixed conversion factor between the two forms, which is itself a finding. The relative potency depends on dose size, frequency, and the assay used.

A practical rule that the evidence supports: at equivalent daily doses, D3 produces a modestly higher 25-hydroxyvitamin D level. The difference at 1,000 IU per day is small enough that it would rarely change a clinical decision. The difference with bolus dosing is larger.

Frequently asked questions

Is D2 less effective at treating deficiency?

At daily doses, the difference is modest and mostly within the range that doesn't change management. Prescription 50,000 IU D2 given weekly for eight weeks remains a standard, effective deficiency protocol.

Why is D3 cheaper?

Lanolin is an abundant byproduct of wool processing. Yeast-derived D2 costs more to produce, and the vegan market is smaller.

Do I need both forms?

No. There's no evidence of synergy, and the body handles them through the same activation pathway.

Does the source of D3 matter?

Lanolin and lichen-derived D3 are the same molecule. The label distinction is about diet, not chemistry.

What about the vegan D3 from lichen?

It's a legitimate D3 source and behaves like other D3 in trials. It's more expensive because the extraction is harder.

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This article is for general information only and does not constitute medical advice. Statements about dietary supplements have not been evaluated by the Food and Drug Administration and are not intended to diagnose, treat, cure, or prevent any disease. Talk with your health care provider before starting any supplement, especially if you have kidney disease or take prescription medication.

Sources

• NIH Office of Dietary Supplements, Vitamin D Fact Sheet for Health Professionals
• Tripkovic L et al., Comparison of vitamin D2 and vitamin D3 supplementation in raising serum 25-hydroxyvitamin D status, AJCN 2012
• Lyles K, How much vitamin D should I take, J Clin Invest 2012
• Trivedi DP et al., Effect of four monthly oral vitamin D3 supplementation on fractures and mortality in men and women living in the community, BMJ 2003
• Sanders KM et al., Annual high-dose oral vitamin D and falls and fractures in older women, JAMA 2010