Evidence explainerVitamin D3 vs D2
Vitamin D3 vs D2: Why the Letter on the Label Changes How Much You Absorb
Your prescription might say D2, your supplement D3. Head-to-head trials say they are not interchangeable, and there is now a plant-free-of-animals D3 too.
Key takeaways
- Head-to-head trials and two meta-analyses find D3 raises blood 25-hydroxyvitamin D more than D2 and keeps it higher longer [1][2][3].
- In a 2024 meta-analysis, daily D2 raised total 25(OH)D about 40% less than D3 [3].
- In a 25-week winter trial at 1,000 IU/day, total 25(OH)D ended 21 nmol/L lower with D2 than with D3 [4].
- Units: 1 mcg of vitamin D equals 40 IU, so 1,000 IU is 25 mcg and the adult upper limit of 4,000 IU is 100 mcg [1].
- D3 is usually made from lanolin (sheep wool), but lichen-derived D3 is an animal-free option [1].
Safety at a glance
From our Vitamin D3 vs D2 monograph. Published interactions and cautions only, each with its source.
Interactions
- Orlistat. With a reduced-fat diet, can reduce vitamin D absorption and lower 25(OH)D.[1]
- Statins. High vitamin D intakes might reduce the potency of these statins because both appear to share a metabolizing enzyme; statins may also reduce vitamin D synthesis.[1]
- Thiazide diuretics. Thiazides reduce urinary calcium loss; combined with vitamin D supplements this might lead to hypercalcemia, especially in older adults and people with reduced kidney function or hyperparathyroidism.[1]
- Corticosteroids. Can reduce calcium absorption and impair vitamin D metabolism; in NHANES 2001–2006, vitamin D deficiency was about twice as common in oral steroid users (11% vs 5%).[1]
Who should be careful
- Pregnancy and breastfeeding. The RDA is the same as for other adults (600 IU), and the 4,000 IU UL applies. Higher amounts should be discussed with a clinician.[1]
- Kidney disease, kidney stones or high calcium. Vitamin D raises calcium absorption. People with reduced kidney function, a history of kidney stones, hyperparathyroidism or high blood calcium face higher hypercalcemia risk, especially with thiazide diuretics.[1]
- High-dose use. Toxicity is almost always from supplements: hypercalcemia, nausea, vomiting, muscle weakness, kidney stones and, in extreme cases, kidney failure and heart rhythm problems. A 3-year trial found lower bone density at 4,000–10,000 IU/day than at 400 IU/day.[1][7]
- Children. ULs are lower for children: 1,000 IU (0–6 months) up to 3,000 IU (4–8 years); 4,000 IU from age 9.[1]
The evidence, graded
Pulled from our monograph evidence tables. Grades follow our evidence-grading policy.
- Grade AImprovedRaising blood 25(OH)D: D3 vs D2Total serum 25(OH)D was 21 nmol/L lower with D2 than with D3; D2 also lowered the 25(OH)D3 metabolite compared with placebo.
Two molecules, one name
Vitamin D comes in two supplement forms: D3 (cholecalciferol), made from lanolin or lichen, and D2 (ergocalciferol), made by irradiating yeast [1]. Both are converted in the body to 25-hydroxyvitamin D, the marker your doctor measures [1].
They are not equal at raising that marker. A 2012 meta-analysis of head-to-head trials found D3 more effective, mainly when given as large single doses [2]. A 2024 meta-analysis of 20 comparisons looked at daily dosing and found D2 raised total 25(OH)D about 40% less than D3, with the gap smallest in people with a BMI over 25 [3].
A winter trial makes it concrete
In New Zealand, 95 healthy adults aged 18 to 50 took 1,000 IU/day of D3, D2 or placebo for 25 weeks over winter [4]. By the end, total 25(OH)D was 21 nmol/L lower with D2 than with D3 [4]. D2 also lowered the body’s own D3-derived metabolite compared with placebo, which is part of why total levels lag [4].
IU, mcg and the numbers on your label
Labels list vitamin D in micrograms, often with IU alongside. The conversion is simple: 1 mcg equals 40 IU [1].
So which should you choose?
For raising blood levels, the evidence favors D3 [1][3]. If you avoid animal products, lichen-derived D3 is an option, or D2 with the understanding that it raises total levels less [1][3]. If a clinician prescribed high-dose D2, ask before switching, because doses and monitoring were chosen for that form.
What neither form did in healthy older adults was lower fracture risk, as the large VITAL trial showed; read does vitamin D protect your bones. The full evidence table is on our vitamin D3 monograph.
Quick answers
Keep reading
Full monographs
Related articles
- Does Vitamin D Protect Your Bones? The 25,871-Person Trial That Surprised Everyone
- Vitamin D3 and K2 Together: Smart Pairing or Marketing? What the Research Actually Shows
- 400 IU of Vitamin E Is Either 268 mg or 180 mg. The "d" or "dl" on the Label Decides
- B12 After 50 and on Metformin: Why Levels Drop, and What the Trials Say About Fixing Them
Browse the full Supplement & Nutrient Encyclopedia or all supplement articles.
References
- [1]Vitamin D: Fact Sheet for Health Professionals. NIH Office of Dietary Supplements, 2025.
- [2]Comparison of vitamin D2 and vitamin D3 supplementation in raising serum 25-hydroxyvitamin D status: a systematic review and meta-analysis. Am J Clin Nutr, 2012.
- [3]Comparison of the Effect of Daily Vitamin D2 and Vitamin D3 Supplementation on Serum 25-Hydroxyvitamin D Concentration (Total 25(OH)D, 25(OH)D2, and 25(OH)D3) and Importance of Body Mass Index: A Systematic Review and Meta-Analysis. Adv Nutr, 2024.
- [4]Long-term vitamin D3 supplementation is more effective than vitamin D2 in maintaining serum 25-hydroxyvitamin D status over the winter months. Br J Nutr, 2013.