D2 vs. D3: Why Form Matters When It Comes To Vitamin D

Everyone seems to be talking about the importance of vitamin D (myself included). In time, it's become the vitamin to rival even the famed vitamin C. 

But when we talk about increasing our vitamin D intake, it's helpful to be clear about the specifics of what we mean, exactly. After all, the body doesn't use all types of vitamin D in the same way; it prefers one kind over another. 

It seems complicated, but that's what we're here for. And the more you know about what type of vitamin D you're supplementing with, the more your body will reap its exceptional benefits. 

"Vitamin D is both a vitamin and a preprohormone (plus a full-on hormone in its active form in the body) essential for healthy bodily function,"* integrative and functional medicine physician Alejandra Carrasco, M.D., previously wrote for mbg. That's after two activation steps in the liver and then the kidneys. Vitamin D can be synthesized in the skin when exposed to the sun. You can also consume the fat-soluble micronutrient from a few sources—plant-based (e.g., algae), animal-derived (e.g., eggs and fish), and even fungi (e.g., UV-irradiated mushrooms). 

Vitamin D can be found in two different forms—D2 and D3—based on source and biochemical structure. "D2 (ergocalciferol) is only derived from plant sources and is often in fortified products. D3 (cholecalciferol) is from animal sources and can be synthesized in the skin from UVB light," shares registered dietitian nutritionist Patricia Bannan, M.S., RDN, author of From Burnout to Balance. 

Vitamin D2 and vitamin D3 also differ structurally—i.e., D3 is far more stable and therefore has superior bioactivity and bioefficacy (more on that later).* Although generally found in animal products, there's one very important caveat to mention: D3 can also be found in algae and lichen, which allows for a plant-based D3 supplement (although algal D3 is much more sustainable for the environment than lichen). 

In a recent Frontiers in Immunology 3scientific review3, researchers determined D2 and D3 influence the expression of genes differently and, therefore, affect the immune system in overlapping but different ways. Some of the findings of this research indicate that it is possible D2 supplementation could even counteract the benefits of D3 intake. The message is that we really don't know the full extent of the differences between D2 and D3 (but we know quite a bit; read on to learn more). 

Form matters when it comes to supplementing with vitamin D. According to Bannan, D3 is the body's preferred form of vitamin D because it's produced in the body naturally and is more efficient at increasing blood levels. In fact, D3 is 87% more potent and effective4 at raising and maintaining serum 25(OH)D levels than D2. And since 25(OH)D levels are your status biomarker, that's a majorly impactful difference.

D2 is significantly less effective because of the structural differences that affect the way the body metabolizes5 the vitamin. Vitamin D2 also has increased catabolism3 (i.e., it's broken down, or metabolized, more quickly) and its metabolites have weaker binding affinity3 to the vitamin-D-binding protein (i.e., the major vitamin D transport protein that carries the nutrient to the rest of the body to confer all those wonderful health benefits we highlighted before).

"These two nutrients are not biologically equivalent or interchangeable," Ashley Jordan Ferira, Ph.D., RDN, mbg's vice president of scientific affairs, previously wrote for mindbodygreen when dissecting D3's scientifically proven superiority over D2. "One is effective (vitamin D3), and the other is way less effective (vitamin D2). Any suggestion that vitamin D3 and D2 are both good options falls into the 'bad science' bucket."

When it comes to bioactivity, vitamin D3 has been shown to raise free 25(OH)D levels—an up-and-coming biomarker that may be more sensitive than total 25(OH)D—with greater efficacy than D26. "This is yet one more compelling piece of evidence cementing the superior bioefficacy of D3 over D2," Ferira concludes.

Overall, if you're looking to increase your vitamin D levels and experience the myriad benefits of sufficient D status, vitamin D3 is the way to go. "Supplementing with D3 instead of D2 will give a greater likelihood of significantly changing vitamin D levels in the body,"* shares registered dietitian Maya Feller, M.S., R.D., CDN, of Brooklyn-based Maya Feller Nutrition. 

So what are some sources of vitamin D3? Most dietary sources of vitamin D3 come from animal foods—including salmon, cod liver oil, trout, and eggs—but there is one significant vegan source of this preferred form of D3: algae.

mindbodygreen leverages sustainable, organic algae in vitamin D3 potency+ (plus, there's a trio of organic avocado, flax, and olive oils for built-in absorption advantage!), making it the perfect supplement for plant-based individuals and omnivores alike.* 

"Unlike some nutrition queries that are somewhat gray and equivocal in nature, when vitamin D3 and vitamin D2 go head-to-head, the winner is clear," concludes Ferira.

To experience the sweeping benefits of this sunshine vitamin, taking 5,000 IU of vitamin D3 paired with a fat (for optimal absorption) is the best option. Because of the limited food sources of vitamin D3 (especially for plant-based eaters), taking a high-quality vitamin D3 supplement, like mbg's vitamin D3 potency+, is the easiest and most effective daily ritual to increase your vitamin D levels (and keep them there).*