Does it matter whether you take vitamin D2 or D3?
It may. A meta-analysis of 11 randomized trials found that taking vitamin D2 lowered blood levels of vitamin D3, the form your body makes on its own, compared with people who did not take it. By the end of the trials, D3 levels were about 18 nmol/L lower (about 7 ng/mL in the units US labs report). Measured as change over the trial, D3 fell about 9 nmol/L (about 4 ng/mL) more than in controls. Whether that changes health outcomes was not tested.
Vitamin D comes in two main forms. Vitamin D3 is the kind your skin makes when sunlight hits it, and it also shows up in animal foods. Vitamin D2 comes from plants and fungi, like certain mushrooms, and it is often cheaper to produce. For years, many people assumed the two forms worked the same way once they were inside a pill. This new research suggests they do not.
When you get your vitamin D checked, the lab measures a marker called 25-hydroxyvitamin D. Doctors use it to judge whether your level is healthy. This study zoomed in on the D3 part of that marker, the piece tied to the form your body produces naturally.
What the data show
The researchers combined the results of 11 randomized controlled trials. This is the strongest kind of study because people are randomly assigned to either a treatment or a comparison group, which cuts down on bias.
The main finding was clear and pointed in one direction. People who took vitamin D2 ended up with lower blood levels of vitamin D3 than people who did not take it. The researchers measured this two ways. Comparing levels at the end of the trials, D3 was about 18 nmol/L (about 7 ng/mL) lower in the D2 groups. Comparing the change from start to finish, D3 fell about 9 nmol/L (about 4 ng/mL) more in the D2 groups. So a D2 pill may raise your total vitamin D number while lowering the D3 part of it.
The authors suggest a regulatory mechanism may speed up the body’s disposal of 25-hydroxyvitamin D when vitamin D levels rise. They say more research is needed to learn whether D2 and D3 change overall vitamin D metabolism in ways that should shape clinical advice.
Dr. Kumar’s Take
I find this study genuinely useful because it answers a common question: does the type of vitamin D really matter? This meta-analysis adds a clear piece to the answer. When you pool 11 trials and see vitamin D2 dragging down D3, that is a pattern worth paying attention to.
I do want to be fair about the limits. A drop of this size is real, but the study measures blood levels, not hard outcomes like fewer infections or fewer broken bones. This is a change in the marker, not yet proof of harm. The authors themselves stop short of recommending D3 over D2 until more research is done.
How strong is the evidence?
The biggest strength here is the study design. Randomized controlled trials reduce bias, and pooling 11 of them gives a clearer picture than any single small trial could. The pooled drop was statistically strong in both analyses, which makes it unlikely to be a fluke of chance.
That said, 11 trials is still a modest evidence base. Those trials likely used different doses, different lengths, and different groups of people, which makes the results harder to compare cleanly. And again, the research tracked a blood marker, not whether people actually got sick less often or felt better. So the finding is clear, but the door is wide open for larger trials to measure real-world health effects.
Practical takeaways
- When you buy a supplement, read the label. Vitamin D3 is listed as cholecalciferol and D2 as ergocalciferol. This study links D2 to lower D3 levels.
- If you follow a vegan diet and want to skip animal-based D3, look for lichen-derived vitamin D3, which is plant-based but still the D3 form.
- Do not assume a higher total vitamin D number on a lab report means you are fully covered, because D2 can lift the total while lowering the D3 part of it.
- Ask your doctor for a 25-hydroxyvitamin D blood test if you are unsure of your level, rather than guessing at a dose on your own.
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FAQs
Is vitamin D3 really better than vitamin D2?
This study cannot settle that. It found that D2 lowered D3 levels in the blood, but it did not measure health outcomes or safety. The authors say more research is needed before this should shape advice to choose D3 over D2. One detail many people miss is that high-dose prescription vitamin D in some countries is the D2 form, so it is worth asking your pharmacist exactly which form you were given.
Can vegans get vitamin D3 without animal products?
Yes. While most D3 supplements come from animal sources like sheep’s wool, there are now D3 products made from lichen, a plant-like organism. These give you the D3 form without animal ingredients, which matters because this research suggests plant-based D2 can drag down your natural D3. If you want to avoid D2 without taking animal products, lichen-derived D3 is an option. Always check the label for the word “cholecalciferol” to confirm it is true D3.
How much does a 9 to 18 nmol/L drop in vitamin D3 actually matter?
The two numbers come from two different analyses: about 18 nmol/L lower at the end of the trials, and about 9 nmol/L more of a fall over the trials. Either way, the effect is meaningful but not dramatic, and its real-world impact likely depends on where you started. For someone already low in vitamin D, losing D3 could push them further from a healthy level. For someone with plenty to spare, the same drop may matter less day to day. The honest answer is that this study measured the blood marker, not symptoms or disease, so no one can yet say it causes harm. It is a reason to know which form you are taking.
Bottom Line
This meta-analysis of 11 randomized trials delivers a simple, practical message: vitamin D2 supplements lowered blood levels of vitamin D3, the form your body makes on its own. By the end of the trials, D3 was about 18 nmol/L (about 7 ng/mL) lower than in controls. The study measured a blood marker, not health outcomes, and the authors say more research is needed before it should change advice on which form to take.
