What if I told you that the vitamin D supplement you’re taking to improve your health could actually be lowering your body’s supply of the most important form of this nutrient? It sounds completely backward, but a new, large-scale scientific review has confirmed this surprising reality. For years, we’ve been told to supplement with vitamin D, especially during darker months, but it turns out the specific type of vitamin D you choose makes a world of difference. Not all vitamin D is created equal, and making the wrong choice might not just be ineffective—it could be actively working against you.
This isn’t about fear-mongering; it’s about empowering you with the latest science so you can make the best choice for your health. We’re going to dive deep into the shocking difference between the two main forms of supplemental vitamin D—D2 and D3. We’ll look at what this new research says, why this is happening in your body, and how you can ensure you’re getting the benefits you’re paying for. It’s time to take a closer look at that supplement bottle on your shelf. (Based on the insights of Felix Harder)
Key Takeaways
- A recent meta-analysis of multiple studies confirmed that taking Vitamin D2 supplements can significantly lower your body’s levels of the more crucial Vitamin D3.
- Vitamin D3 (cholecalciferol) is the form your body naturally produces from sunlight. It is more potent, more stable, and more effective at raising and maintaining healthy vitamin D levels than D2.
- Most standard vitamin D blood tests measure your total vitamin D level, which combines D2 and D3. This can hide a drop in your D3 levels caused by D2 supplementation, giving you a false sense of security.
- When buying a supplement, you should always look for Vitamin D3 on the label. Avoid Vitamin D2 (ergocalciferol), which is a less effective and potentially counterproductive choice.
- For those following a vegan diet, high-quality Vitamin D3 supplements derived from lichen are now widely available, so there is no need to settle for the inferior D2 form.
1. The Surprising New Research: What a Major Study Revealed
Recently, the scientific community got a major update from a new meta-analysis—a type of “super-study” that pools together the data from many previous high-quality studies to find a more powerful and reliable conclusion. This particular analysis looked at several randomized controlled trials, the gold standard of medical research, to see what happens when people supplement with Vitamin D2.
The results were startling. The paper, titled “Effect of Vitamin D2 Supplementation on 25-hydroxyvitamin D3 Status,” found that when people took Vitamin D2 supplements, their blood levels of Vitamin D3 went down. To be clear: they took one form of the vitamin, and their levels of the other, more important form, dropped significantly.
Let’s look at the numbers to see what this means for you. Across the studies, people taking D2 had, on average, about 18 nmol/L less Vitamin D3 in their blood compared to people who took no supplement at all. To put that in perspective, if your D3 level was at a healthy 40 nmol/L before you started, taking a D2 supplement could cause it to drop into the low 30s—a meaningful reduction that could push you toward deficiency. The problem is, you’d likely never know it was happening based on your standard lab work.
2. Understanding the Players: Vitamin D2 vs. Vitamin D3
To understand why this happens, you first need to know that “Vitamin D” isn’t a single substance. It’s a family of related compounds. The two most common forms you’ll encounter are D2 and D3.
- Vitamin D2 (Ergocalciferol): This is the plant- and fungus-based form of vitamin D. It’s produced in some mushrooms when they are exposed to UV light. Commercially, it’s often made by irradiating yeast. Because it’s generally cheaper to produce, Vitamin D2 is often found in lower-cost supplements and is frequently used to fortify foods like plant-based milks, orange juice, and breakfast cereals.
- Vitamin D3 (Cholecalciferol): This is the form of vitamin D that your own body produces when your skin is exposed to sunlight. It’s often called the “sunshine vitamin” for this reason. When it comes to supplements, D3 is traditionally sourced from lanolin, a waxy substance from sheep’s wool. However, as we’ll discuss later, excellent vegan options from lichen are now available. Your body is designed to use D3, and research has consistently shown it’s the superior form.
For a long time, many treated these two forms as if they were interchangeable. This new research is the final nail in the coffin for that outdated idea.
3. Why Does D2 Lower Your D3 Levels? The Science Explained
So, what is the biochemical drama happening inside your body that causes D2 to push out D3? Researchers have proposed a couple of key theories, and they both come down to competition.
First, there’s the theory of enzyme competition in the liver. Think of your liver as a processing plant with a limited number of workers (enzymes) that handle vitamin D. Both D2 and D3 have to be converted by these same enzymes to become active in your body. When you flood your system with a large amount of Vitamin D2, these enzymes get preoccupied with processing it. This intense focus on D2 appears to speed up the breakdown and clearance of the existing Vitamin D3 in your system. It’s like the workers are so busy with the new D2 shipment that they start clearing out the D3 to make space, leaving you with less of it.
Second, there’s the idea of competition for binding proteins in your blood. To travel through your bloodstream and remain stable, vitamin D needs to attach to a specific carrier called a vitamin D-binding protein. Think of these proteins as seats on a bus. Vitamin D3 is known to bind very tightly to these seats, which helps it stay in circulation longer. Vitamin D2, however, binds more loosely. When you introduce a lot of D2, it crowds the bus, competing for seats. This competition can knock D3 off its seat, leaving it unstable and more likely to be filtered out and removed from your body much faster.
Whatever the exact mechanism, the result is the same: supplementing with D2 doesn’t just add a weaker form of vitamin D to your system; it actively depletes your stores of the stronger, more natural D3.
4. The “Hidden” Problem with Your Blood Test
This is perhaps the most concerning part of the D2 versus D3 issue. When your doctor orders a vitamin D test, they are almost always testing for a marker called 25-hydroxyvitamin D. This is considered the best indicator of your body’s vitamin D stores. However, this number represents your total vitamin D—it’s the sum of both 25-hydroxyvitamin D2 and 25-hydroxyvitamin D3.
Here’s the deceptive scenario: You start taking a Vitamin D2 supplement. Your blood levels of D2 go way up. At the same time, your levels of the more important D3 go down. When you get your blood test, the lab adds the two together. The huge increase in D2 can easily mask the drop in D3, so your total 25-hydroxyvitamin D level might look normal or even high. You and your doctor would assume the supplement is working perfectly, while under the surface, your body is losing the form of vitamin D it actually prefers and uses most effectively.
5. Why D3 is the Undisputed Champion
Science has been pointing to the superiority of Vitamin D3 for years, and this new analysis just reinforces it. D3 is more potent, meaning it’s much better at raising your total vitamin D levels compared to the same dose of D2—studies suggest it’s anywhere from 1.7 to 3 times more effective.
Furthermore, D3 is more stable and has a longer half-life. This means it sticks around in your body for a longer period, providing a more sustained and reliable supply. D2, on the other hand, is cleared from the body more quickly. This is why D3 is far more effective at maintaining your vitamin D levels over the long term.
Interestingly, studies show that taking Vitamin D3 can also cause a slight reduction in D2 levels, but this effect is much, much weaker than the D3-lowering effect of D2. The bottom line is that your body is built for D3, and it’s the form that delivers the most powerful and lasting benefits for your immune system, bone health, and overall well-being.
6. How to Choose the Right Vitamin D Supplement
This all leads to a very simple, practical action you can take right now. Go to your medicine cabinet and look at your vitamin D supplement. Turn the bottle around and read the ingredients list on the back. You are looking for one of two names:
- Choose this: Vitamin D3 (as cholecalciferol)
- Avoid this: Vitamin D2 (as ergocalciferol)
If your supplement contains D2, you are not getting the best value for your money or your health. It’s worth finishing the bottle if you wish, but your next purchase should absolutely be a D3 supplement. Also, be a savvy consumer when it comes to fortified foods. Since D2 is cheaper, it’s the form often added to cereals, juices, and plant milks. While this isn’t a reason to avoid these foods entirely, you shouldn’t rely on them as your primary source of effective vitamin D.
7. A Note for Vegans: You Don’t Have to Settle for D2
For a long time, Vitamin D2 was promoted as the go-to option for vegans because D3 was traditionally derived from sheep’s wool. This left many health-conscious individuals in a bind, forced to choose the inferior form to align with their ethics. Thankfully, that is no longer the case.
In recent years, a game-changing source of vegan Vitamin D3 has become widely available: lichen. Lichens are unique, plant-like organisms that are a natural, sustainable, and completely plant-based source of cholecalciferol. This means you can now get the superior, more potent form of Vitamin D3 without compromising your vegan lifestyle. There is no longer any reason for anyone, vegan or not, to supplement with Vitamin D2.
Conclusion
The evidence is overwhelming, and the conclusion is simple. Vitamin D2 and Vitamin D3 are not the same, and they are not interchangeable. Taking a Vitamin D2 supplement is not just a less effective strategy; it’s a counterproductive one that actively lowers your body’s levels of the more potent and natural Vitamin D3. To truly support your health, protect your immune system, and maintain strong bones, the choice is clear. Always check the label and make sure you are taking Vitamin D3 (cholecalciferol). Your body will thank you for it.
Source: Felix Harder