Vitamin D2 vs D3: new research says D2 can lower your D3 level
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Short answer: both vitamin D2 and vitamin D3 raise your vitamin D level, but D3 does it more strongly and for longer. A 2025 review of randomised trials also found that taking D2 lowers the amount of D3 in your blood. For most people choosing a supplement, D3 is the better pick, and the only way to see how your own body responds is to test.
What the new research found
Researchers from the University of Surrey, the John Innes Centre and Quadram Institute Bioscience pooled randomised controlled trials that measured blood vitamin D3 (25(OH)D3) in people taking vitamin D2. They included 20 trials in their review, 11 of which had data suitable for the main meta-analysis (Brown et al., 2025).
Compared with people who didn't take D2, those taking D2 had lower blood D3:
- about 18 nmol/L lower (roughly 7 ng/mL) at the end of the trials, and
- about 9 nmol/L lower (roughly 4 ng/mL) when looking at the change over each trial.
Because these were randomised trials, the authors say the drop in D3 is likely caused by the D2. Their leading explanation is that when total vitamin D rises, the body speeds up the breakdown of what's circulating, and some of that breakdown comes out of the D3 you already had (Brown et al., 2025; University of Surrey, 2025).
The lead researcher, Dr Emily Brown, said the findings suggest that "subject to personal considerations, vitamin D3 supplements may be more beneficial for most individuals over vitamin D2" (University of Surrey, 2025).
Does that mean D2 doesn't work?
No. D2 still raises the D2 part of your vitamin D level, and a separate 2026 meta-analysis of 26 trials found it still has measurable effects in the body, including lowering parathyroid hormone (Lai et al., 2026). The issue is efficiency. Earlier pooled analyses found D3 raises total 25(OH)D more than D2 does (Tripkovic et al., 2012), and the US National Institutes of Health notes that D3 tends to raise levels more and keep them up for longer (NIH Office of Dietary Supplements).
So the trade looks like this: with D2, some of what you gain on the D2 side you give back on the D3 side.
D2 vs D3 at a glance
| Vitamin D2 (ergocalciferol) | Vitamin D3 (cholecalciferol) | |
|---|---|---|
| Where it comes from | Fungi and yeast exposed to UV light, including UV-treated mushrooms | Made in your skin from sunlight; supplements from lanolin (sheep's wool) or, for vegans, lichen |
| Raises total vitamin D | Yes, but less on average | Yes, more on average and for longer |
| Effect on the other form | Lowers blood D3 (about 9–18 nmol/L in pooled trials) | Not the focus of this review |
| Vegan options | Yes | Yes (lichen-derived) |
Where Australians actually get D2
Most vitamin D supplements on Australian shelves are D3, so for many people this research is reassuring rather than alarming. D2 mostly turns up in two places:
- Vitamin D mushrooms. Mushrooms make D2 when exposed to UV light. Testing of Australian supermarket mushrooms found about 2.3 µg of vitamin D per 100 g in regular mushrooms and about 26.6 µg per 100 g in UV-treated "vitamin D mushrooms" (FSANZ, 2015). They're a genuinely useful food, and a meal of mushrooms is very different from taking a concentrated D2 supplement every day.
- Some plant-based supplements. Vegan products may use mushroom-derived D2. If you want a vegan option, lichen-derived D3 is now widely available, which is exactly the point the Surrey team made about plant-based D3 (University of Surrey, 2025).
Check the label: it will say "ergocalciferol" (D2) or "cholecalciferol" (D3). For more on dose, timing and taking it with food, see how to take vitamin D supplements, and for food sources see foods high in vitamin D.
Why the type of test matters if you take D2
Your vitamin D result is 25(OH)D, which is the sum of 25(OH)D3 and 25(OH)D2. Some quicker test methods don't pick up the D2 part fully, which can make your level look lower than it is if you take D2. A lab test by LC-MS/MS measures the two forms separately, so you see your true total and how much of it is D2 versus D3.
Our Vitamin D Test uses LC-MS/MS and reports D3 and D2 separately, so whichever supplement you take, it's counted properly. If you're switching from D2 to D3 (or the other way), that split shows you what actually changed. More on the method in pharmacy rapid tests vs lab-based testing.
If you're thinking of switching
- Test first so you have a baseline. Our vitamin D levels chart for Australia explains what the numbers mean.
- Make one change, such as moving from D2 to D3 at a similar dose. Don't go above 4,000 IU a day unless your doctor advises it (see can you take too much vitamin D?).
- Retest after about 3 months. Levels take 8–12 weeks to settle at a new dose (how long vitamin D takes to work). The Vitamin D 2-Pack covers your baseline and your retest.
If you've been prescribed a particular form or dose by your doctor, talk to them before changing it.
What we still don't know
The research shows a clear difference in blood levels. It doesn't yet show whether that difference changes long-term health, and the authors say more work is needed on how the two forms are processed (Brown et al., 2025). That's why measuring your own level, rather than guessing, is the practical step.
FAQ
Is vitamin D3 better than D2?
For raising and keeping up your blood vitamin D level, the evidence favours D3. D3 raises total 25(OH)D more on average, and a 2025 meta-analysis found that D2 lowers blood D3 by about 9–18 nmol/L.
Does vitamin D2 lower vitamin D3?
Yes, according to a 2025 review of randomised trials in Nutrition Reviews. People taking D2 had lower blood D3 than people who didn't. D2 still adds to your total, but less efficiently than D3.
Are vitamin D mushrooms D2 or D3?
Mostly D2. Mushrooms convert ergosterol to vitamin D2 when exposed to UV light. Australian UV-treated mushrooms tested at about 26.6 µg of vitamin D per 100 g.
Is there a vegan vitamin D3?
Yes. Vitamin D3 made from lichen is plant-based and widely available in Australia.
Will a vitamin D test pick up D2?
An LC-MS/MS lab test measures 25(OH)D2 and 25(OH)D3 separately and adds them for your total. Our Vitamin D Test reports both.
How long after switching should I retest?
About 3 months. It takes 8–12 weeks for your level to settle after a change in supplement or dose.
Sources
- Brown EIG, Darling AL, Robertson TM, et al. Effect of vitamin D2 supplementation on 25-hydroxyvitamin D3 status: a systematic review and meta-analysis of randomized controlled trials. Nutrition Reviews, 2025. doi:10.1093/nutrit/nuaf166
- University of Surrey. "Vitamin D3 concentrations are lowered by a common vitamin D supplement." 23 September 2025. surrey.ac.uk
- ScienceDaily. "Scientists warn a popular vitamin D supplement may have a hidden downside." 8 October 2026. sciencedaily.com
- Lai J, Yu X, Prabahar K, et al. Effects of vitamin D2 (ergocalciferol) on parathyroid hormone, calcium, and phosphorus in humans: a systematic review and meta-analysis of RCTs. Nutrition Reviews, 2026;84(3):571. doi:10.1093/nutrit/nuaf102
- Tripkovic L, Lambert H, Hart K, et al. Comparison of vitamin D2 and vitamin D3 supplementation in raising serum 25-hydroxyvitamin D status: a systematic review and meta-analysis. American Journal of Clinical Nutrition, 2012;95(6):1357–64. doi:10.3945/ajcn.111.031070
- NIH Office of Dietary Supplements. Vitamin D fact sheet for health professionals. ods.od.nih.gov
- Food Standards Australia New Zealand. Vitamin D mushrooms (NMI analysis of Australian retail mushrooms, 2015). foodstandards.gov.au