I'm A PhD & RD: Here's Why Vitamin D3 Is Far Superior To D2

Vitamin D has gained much well-deserved attention over the past year. After all, this nutrient is essential to our immune system.* Like me, I know many of you are vitamin D fans. Sadly, that vitamin D love (and money) can go to waste if you're not taking the right form of vitamin D. D3 or D2? That is the question. 

Unlike some nutrition queries that are somewhat gray and equivocal in nature, when vitamin D3 (cholecalciferol) and vitamin D2 (ergocalciferol) go head-to-head, the winner is clear. Allow me to use an analogy to explain.

At the Olympics recently, two phenomenal high jumpers from Qatar and Italy shared a heartwarming conclusion to their final event (where they jumped almost 8 feet in the air!) by choosing to share the Olympic gold rather than have a jump-off. They both left Tokyo with gold medals. Vitamin D3 and D2 are...nothing like that. 

To wrap my Olympics nutrition visual: Vitamin D3 is on the middle podium with its anthem playing loud and clear, whereas vitamin D2 didn't medal at all. Harsh but true. Before I get granular on why D3 triumphs over D2, let's recap why vitamin D should be top of mind in the first place.

Now that we understand why daily vitamin D supplementation is critical, there's one final layer to consider: form. Your options are vitamin D3 or vitamin D2.* And here's the bottom line: These two nutrients are not biologically equivalent or interchangeable. Any suggestion that vitamin D3 and D2 are both good options falls into the "bad science" bucket.

Vitamin D3 and D2 have historically been differentiated by their origin: animal versus plant. Vitamin D3 is almost always animal-derived, from lanolin from sheep's wool. This is a fine source of D3 and the most common in the market. In contrast, vitamin D2 is plant-derived from irradiated yeast and mushrooms mostly. 

But that's old news. Innovative technologies in the past several years have developed vitamin D3 options from plant origins (I see you, vegans), specifically from lichen and algae, the latter algal source being significantly more sustainable and pure. Albeit rare, there are even certified organic plant-origin varieties of D3.

Instead of differentiating vitamin D3 versus D2 by origin or source, I would like to propose a new method of comparison: One is effective (vitamin D3), and the other is way less effective (vitamin D2). And here's why: Vitamin D3 has superior bioefficacy, bioactivity, and stability, compared to vitamin D2.*

What I mean here is that vitamin D3 is significantly better at helping raise your total 25(OH)D levels (aka: the biomarker for vitamin D status) and keeping them there.*

Why does this ultimately matter? Well, aside from 25(OH)D being the primary indicator of whole-body vitamin D status, this compound is converted into 1,25(OH)2D (the activated form of vitamin D) for its many essential actions in cells, tissues, and organs throughout the body—like our bones, muscles, immune cells, brain, etc.* 

The fact that vitamin D3 is way better than D2 at helping us achieve and maintain vitamin D sufficiency has been demonstrated by loads of robust research in humans. I'm talking about numerous randomized, placebo-controlled, and double-blind clinical trials; so many, in fact, that a landmark systematic review and meta-analysis2 in the American Journal of Clinical Nutrition concluded that "vitamin D3 is more efficacious at raising serum 25(OH)D concentrations than is vitamin D2."*

How much better is vitamin D3 at increasing 25(OH)D levels? Some studies estimate that the potency of D3 is a whopping 87% higher than D23. This effect of vitamin D3 supplementation superiority has been proved over and over:* Let me share a few prime examples:

There is also evidence that vitamin D3 is better than D2 when it comes to bioactivity, as it's been shown to raise free 25(OH)D levels8 with greater efficacy. This "free" marker is an emerging status measure of vitamin D bioactivity, and it may be more sensitive than total 25(OH)D. 

Next, vitamin D2 metabolites have weaker binding9 to the vitamin D binding protein, which binds the nutrient and carries it throughout the body to do its job.

And finally, vitamin D2 demonstrates reduced hydroxylation of vitamin D37 (a necessary activation step in normal vitamin D metabolism) while also increasing the catabolism (aka breakdown) of 25(OH)D3 for excretion. These competitive mechanisms have been demonstrated with vitamin D2 supplementation at multiple doses (1,000 I.U./day5, 2,000 I.U./day6, 100,000 I.U./month7), and the ultimate effect is reduced 25(OH)D3 levels. Talk about counterproductive.

In addition to superior bioefficacy and bioactivity, vitamin D3 exhibits superior stability over D29—meaning, it lasts longer in the body. In fact, vitamin D3 has been shown in clinical research to have a significantly longer half-life10 (and thus extended opportunity for its biological effects in the body) than its inferior counterpart (D2).

Sorry, vitamin D2 simply isn't suitable for supplementation. Now, you can see why vitamin D2 does not "medal" in the nutrition "Olympics." In a bold but scientifically accurate conclusion9, scientists who have researched vitamin D for their entire academic careers put it this way: Due to the superior bioefficacy of vitamin D3, "vitamin D2 should not be regarded as a nutrient suitable for supplementation." 

I concur and wish nutritionists and health media reporters would stop talking about D3 and D2 as equally suitable options. They're not. D3 equals gold. Spread the word.