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 effective 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 metabolizes the vitamin. Vitamin D2 also has increased catabolism (i.e., it's broken down, or metabolized, more quickly) and its metabolites have weaker binding affinity 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 D2. "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, MS, RD, CDN of Brooklyn-based Maya Feller Nutrition.