Vitamin D2 vs D3 (2026): Which Should You Take?

Q: Is vitamin D2 or D3 better?

Vitamin D3 (cholecalciferol) is significantly better than D2 (ergocalciferol). A meta-analysis of 7 RCTs found D3 raises blood 25(OH)D levels approximately 2-3 times more effectively than D2 at the same dose. D3 also has a longer half-life in the body, maintaining stable blood levels for weeks vs days for D2. Most clinical guidelines now recommend D3 exclusively. The only advantage of D2 is that it is plant-derived (suitable for strict vegans), while most D3 comes from lanolin (sheep wool) — though vegan D3 from lichen is now available.

Q: Why do doctors still prescribe vitamin D2?

Historical inertia. Prescription vitamin D (Drisdol) is D2 at 50,000 IU, which was the only high-dose option available for decades. D3 is now available in equivalent high-dose formulations both OTC and by prescription. Many endocrinologists and updated clinical guidelines have shifted to recommending D3, but some prescribing habits lag behind the evidence.

Q: How much vitamin D3 should I take?

For maintenance (if you are not deficient): 1,000-2,000 IU/day of D3. For correcting deficiency (25(OH)D below 20 ng/mL): 4,000-5,000 IU/day for 8-12 weeks, then retest. The NIH tolerable upper limit is 4,000 IU/day, though many experts consider up to 5,000 IU safe for adults. If taking 4,000+ IU, consider adding vitamin K2 (MK-7) to help direct calcium appropriately.

By Verified Supplement Data · Published March 15, 2026 · Methodology · About Us

Short answer: Take D3, not D2. Vitamin D3 (cholecalciferol) is 2-3x more effective than D2 (ergocalciferol) at raising blood 25(OH)D levels. D3 has a longer half-life, maintains more stable blood levels, and is what your body naturally produces from sunlight. The only reason D2 still exists in the market is historical — it was the only form available for decades.

Exception: Strict vegans may prefer D2 (plant-derived) or vegan D3 from lichen.

Head-to-Head Comparison

Vitamin D2 (ergocalciferol) vs D3 (cholecalciferol): key differences
Factor	Vitamin D2	Vitamin D3
Chemical name	Ergocalciferol	Cholecalciferol
Source	Fungi, yeast (plant-derived)	Lanolin (sheep wool), lichen (vegan option), fish liver oil
Effectiveness at raising blood levels	Baseline	2-3x more effective at raising 25(OH)D
Half-life	~2-3 days	~2-3 weeks (much more stable)
Natural to humans?	No — humans don't produce D2	Yes — your skin makes D3 from UVB sunlight
Available high-dose?	50,000 IU (prescription Drisdol)	50,000 IU (OTC and prescription)
Vegan?	Yes (plant-derived)	Most: No (lanolin). Vegan options from lichen exist.
Cost	Similar to D3	Similar to D2 — no price advantage to D2
Expert recommendation	Outdated — most guidelines now prefer D3	Recommended by most endocrinologists and updated guidelines

The Evidence: Why D3 Wins

Bioavailability and Blood Level Raising

Multiple studies have compared D2 and D3 head-to-head. The consistent finding is that D3 raises serum 25-hydroxyvitamin D [25(OH)D] — the standard measure of vitamin D status — significantly more than D2 at equivalent doses:

A 2024 systematic review and meta-analysis of 20 comparative RCTs (PMID: 37865222) found D2 raised total 25(OH)D 10.39 nmol/L (40%) less than D3, even with daily dosing. BMI was the strongest response modifier — the gap narrowed in overweight individuals.
A 2022 transcriptome study (PMID: 35281034) showed D2 and D3 are not functionally equivalent — only D3 stimulated type I and type II interferon activity (immune defense). Most gene expression changes were vitamin-specific, not shared.
Even single large doses (50,000 IU) show D3 produces a higher, more sustained peak than D2

Stability in the Body

D3's longer half-life (~2-3 weeks vs ~2-3 days for D2) means:

Blood levels remain stable between doses
Missing a day or two doesn't cause the same dip as with D2
Weekly dosing is a viable option with D3 (not recommended with D2)

Why D2 Still Exists

Prescription vitamin D (Drisdol) has historically been D2 at 50,000 IU. When a doctor prescribes "vitamin D," the pharmacy may fill it with D2 by default. This is a legacy issue — D3 is now available in equivalent high-dose formulations. If your doctor prescribed D2, it's worth asking if you can switch to D3.

Dosing Guide

Vitamin D3 dosing by situation
Situation	D3 Dose	Duration	Notes
Maintenance (not deficient)	1,000-2,000 IU/day	Ongoing	Maintains levels if already adequate
Mild deficiency (20-29 ng/mL)	2,000-4,000 IU/day	8-12 weeks, then retest	Most common scenario
Moderate deficiency (<20 ng/mL)	4,000-5,000 IU/day	8-12 weeks, then retest	Consider adding K2 at this dose
Severe deficiency (<10 ng/mL)	50,000 IU/week (Rx) or 5,000-10,000 IU/day	8-12 weeks, then retest	Should be under medical supervision
NIH tolerable upper limit	4,000 IU/day	—	Many experts consider 5,000 IU safe for adults

Get tested. Unlike magnesium (where blood tests are unreliable), vitamin D blood tests [25(OH)D] are accurate and widely available. Normal range: 30-80 ng/mL. Below 20 ng/mL is deficient. Below 30 ng/mL is insufficient. Ask your doctor for a test — it's a simple blood draw.

What About K2?

Vitamin K2 (menaquinone-7, or MK-7) helps direct calcium to bones and teeth rather than arteries. The concern: high-dose vitamin D increases calcium absorption, and without adequate K2, some of that calcium may deposit in arteries.

If taking <2,000 IU/day D3 — K2 supplementation is probably unnecessary if you eat some fermented foods or leafy greens
If taking 4,000+ IU/day D3 — adding K2 (100-200mcg MK-7) is a reasonable precaution
Many D3 supplements now include K2. These combination products are convenient.

See our upcoming detailed guide on Vitamin D + K2 co-supplementation.

Frequently Asked Questions

Is vitamin D2 or D3 better?

D3 is significantly better. It's 2-3x more effective at raising blood levels, has a longer half-life (weeks vs days), and is what your body naturally produces from sunlight. Take D3 unless you need a vegan option (in which case, look for D3 from lichen).

Why do doctors still prescribe vitamin D2?

Historical inertia. Prescription vitamin D (Drisdol) has been D2 for decades. D3 is now available in equivalent high-dose formulations. Ask your doctor about switching — most updated guidelines recommend D3.

How much vitamin D3 should I take?

Maintenance: 1,000-2,000 IU/day. Correcting deficiency: 4,000-5,000 IU/day for 8-12 weeks. Get a blood test [25(OH)D] to know your baseline. NIH upper limit is 4,000 IU/day, but many experts consider 5,000 IU safe.

Related Guides

Vitamin D Supplement Guide — Full hub page
Best Magnesium Supplement — Another commonly deficient mineral
Signs of Magnesium Deficiency — Often co-occurs with vitamin D deficiency

Sources

van den Heuvel EG, et al. "Comparison of the Effect of Daily Vitamin D2 and Vitamin D3 Supplementation on Serum 25-Hydroxyvitamin D Concentration: Systematic Review and Meta-Analysis." Adv Nutr. 2024;15(1):100133. PMID: 37865222
Durrant LR, et al. "Vitamins D2 and D3 Have Overlapping But Different Effects on the Human Immune System." Front Immunol. 2022;13:790444. PMID: 35281034
Tripkovic L, et al. "Comparison of vitamin D2 and vitamin D3 supplementation in raising serum 25-hydroxyvitamin D status." Am J Clin Nutr. 2012;95(6):1357-1364. PMID: 22552031
Heaney RP, et al. "Vitamin D3 is more potent than vitamin D2 in humans." J Clin Endocrinol Metab. 2011;96(3):E447-452. PMID: 21177785
NIH Office of Dietary Supplements. "Vitamin D: Fact Sheet for Health Professionals." ods.od.nih.gov