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.
Why do you need vitamin D?
Previously pigeon-holed as a bone health nutrient, vitamin D is that and so much more. Research in the past 40 years has uncovered that this hormone-like essential fat-soluble micronutrient affects our total-body health, including our bones and teeth, muscles, immune function, fertility, and mood,* to name a few.
Despite its importance, there is clear data demonstrating how widespread the vitamin D gap is in our country. For instance, we know that the large majority (93%) of American adults are not even consuming 400 IU of vitamin D1 from their daily diet. Extrapolating from that nationally representative stat, I guesstimate 99% of us are failing to eat at least 3,000 I.U. of vitamin D (the minimum intake level to achieve vitamin D sufficiency, i.e., serum 25(OH)D level > 30 ng/ml) from food alone. This is where supplementation can help—but only if you choose the right form.
Why all forms of vitamin D aren't created equal.
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.
So, where might you find vitamin D3 vs. D2?
- Your skin creates vitamin D3 from UVB sun exposure.
- Vitamin D2 and D3 are both found in food sources (D2: irradiated yeast and mushrooms; D3: oily fish and fish liver oils, egg yolk).
- Vitamin D3 and D2 sources are both used in food fortification (i.e., dairy, orange juice, breakfast cereals).
- Vitamin D3 and D2 are both used in dietary supplements, although D3 is more common.
- Vitamin D2 is the form found in the prescription medication form of vitamin D.
Benefits of vitamin 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.*
Vitamin D3 has superior bioefficacy.
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:
- In this U.K. food fortification study4, where South Asian and European women consumed 600 I.U. of vitamin D3 or D2 daily for three months.
- A study of New Zealand adults5 who consumed 1,000 I.U. daily of D3 or D2 for six months during the winter.
- This wintertime study from Germany6 with adults who supplemented with 2,000 I.U. of D3 or D2 for two months.
- A bolus-dose study of U.K. adults7 who took 100,000 I.U. of D3 or D2 monthly over four months.
- A study conducted in U.K. adults8 who took 50,000 I.U. of D3 or D2 twice a week for five weeks.
- This clinical study of American adults3 who consumed 50,000 I.U. per week of D3 or D2 for three months.
Vitamin D3 has superior bioactivity.
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.
Vitamin D3 has superior stability.
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.
Ashley Jordan Ferira, Ph.D., RDN is Vice President of Scientific Affairs at mindbodygreen. Ashley received her B.A. in Biological Basis of Behavior from the University of Pennsylvania (along with a double minor in Nutrition and Music) and Ph.D. in Foods and Nutrition from the University of Georgia. Her research contributions span vitamin D, cardiometabolic health, bone density, and weight management. Ferira is a nutrition scientist and dietitian with experience in nutrition product innovation and development, scientific affairs, education, communications, and SEO writing for global firms, including Nature Made, Metagenics, Three Ships, and mindbodygreen.
In addition to her mindbodygreen contributions, Ferira is published in Health, Metagenics Institute, American Family Physician, The Journal of Clinical Endocrinology & Metabolism, and Osteoporosis International. She has a passion for the translation of evidence-based science into innovative and high-quality products and information that help people lead healthier lives. She is a believer in compassionate, informed, and personalized approaches to nutrition, health care, and wellness. Ashley lives in beautiful Charleston, South Carolina, where she was born and raised. Whether savoring an orchestral performance or delectable meal at a local restaurant, you will find her enjoying Charleston’s cultural and culinary arts with family and friends.