Vitamin D2 vs D3 supplements: D2 may lower your D3
Vitamin D2 vs D3 supplements: a review of randomized trials found D2 may lower D3 in your blood. Here are the numbers and what we still don't know.
The 30-second summary
- A 2025 review of randomized trials found that people given vitamin D2 had about 9 to 18 nmol/L less vitamin D3 in their blood than people who were not.
- Both forms raise vitamin D, but the evidence leans toward D3 raising it more and keeping it up longer.
- The study only measured blood levels; we don't yet know whether the drop affects health.
Vitamin D2 and D3 supplements differ mainly in where they come from and how well they work. D2 is usually made from fungi or yeast, while D3 is the same form your skin makes in sunlight. Both raise vitamin D in your blood, but the evidence leans toward D3 raising it more and keeping it up longer.
Now a 2025 review in the journal Nutrition Reviews adds another difference: taking D2 may lower the D3 already in your blood. Here is what the researchers found, how they found it, and what is still unknown.
What did researchers find?
The researchers pooled randomized trials in which some people were given vitamin D2 and compared them with groups that weren't, who got a placebo or no supplement. The result: people who took D2 had lower vitamin D3 in their blood, and the difference was statistically clear.
The size of the drop depended on how it was measured. Comparing the two groups at the end of the trials, the gap averaged about 18 nmol/L. Looking at how much levels changed during the trials, it was about 9 nmol/L. That is why the drop is described as roughly 9 to 18.
This doesn't mean D2 pulls vitamin D out of your body or that it is harmful. D2 raises its own form in the blood and adds to your total vitamin D. The surprise is that raising one form seemed to go along with a fall in the other. Why is not settled: one proposed explanation is that the body speeds up the removal of vitamin D when levels rise, but that is still a hypothesis.
How was the study done?
This kind of study doesn't recruit new volunteers. It gathers the results of earlier studies and analyzes them together. A team from the University of Surrey, the John Innes Centre and the Quadram Institute in the UK searched the PubMed database for research published between 1975 and early 2023 and found 202 articles. Twenty fit the review, and 11 had data suitable for the main analysis, covering 655 people: 342 who took D2 and 313 in comparison groups that got a placebo or nothing. All were randomized trials, meaning people were assigned to groups by chance, which makes the comparison fairer.
We rate evidence by study design, not by how exciting the result is. How we rate evidence
What does it mean for you?
The main message: the type of vitamin D on your supplement label may matter. Both forms raise vitamin D in the blood, and information from the US National Institutes of Health says D3 tends to raise it more and keep it up longer. The study's lead researcher said that, depending on personal circumstances, D3 may be more beneficial for most people.
Still, this result doesn't make D2 a bad choice. A separate 2026 review of 26 trials found that D2 lowered parathyroid hormone and slightly raised blood calcium, so it clearly still acts in the body. If you take a supplement your doctor prescribed or for a specific reason, don't change it on your own; ask your doctor first. And if you chose D2 because it is animal-free, know that animal-free D3, such as D3 from lichen, also exists.
But keep in mind
- The results are about vitamin D3 levels in the blood, not about diseases or long-term health.
- A 2026 review of 26 trials found that D2 still has clear biological effects, so lower D3 doesn't mean D2 is useless.
- The reason for the drop isn't confirmed; the proposed explanation is still a hypothesis.
- The main analysis pooled only 11 of the 20 studies (655 people), and the size of the drop depended on how it was calculated.
FAQ
Does vitamin D2 lower vitamin D3?
According to a 2025 review of randomized trials, yes, on average: people who took D2 had about 9 to 18 nmol/L less D3 in their blood than those who didn't. Whether this drop matters for health is not yet known.
Which is better, vitamin D2 or D3?
Both raise vitamin D in the blood, but the accumulated evidence favors D3 for a larger increase that lasts longer. It hasn't been shown that this changes health outcomes, and the right choice for you is one to discuss with your doctor.
Where do vitamin D2 and D3 supplements come from?
D2, also called ergocalciferol, is usually made from fungi or yeast exposed to ultraviolet light. D3, or cholecalciferol, is the form your skin makes in sunlight; in supplements it often comes from lanolin in sheep's wool, and animal-free D3 from lichen is also available.
Is vitamin D2 harmful?
This study doesn't say so. D2 raises its own form of vitamin D in the blood, and another review of 26 trials found it has clear biological effects. The study measured blood levels only, not harms or diseases.
Sources
- 1
- 2Scientists warn a popular vitamin D supplement may have a hidden downsideScienceDaily · 2026
- 3Effect of vitamin D2 supplementation on 25-hydroxyvitamin D3 status (publication listing)John Innes Centre · 2025
These are the original sources; we only explain them. Read them yourself.
Science information for education only; it does not replace medical advice.
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