They are thought to be interchangeable. Ergocalciferol is made by irradiating mushrooms with UV light; like people, they “tan” and produce vitamin D. Cholecalciferol is derived from the rich waxy lanolin “waterproofing” in sheep’s wool.

I’ve long recommended that people take D3, in the belief that it is somewhere around 50% more bio-available than D2. If that were the sole knock on ergocalciferol, one could simply take more of the D2 version and get comparable results. But there’s more to the story.

Some dyed-in-the-wool (excuse the pun) vegans prefer D2 because, not only do they not eat meat and poultry, or even wear leather, but they also prefer to eschew any product derived from what they view as animal exploitation, for ethical reasons.

Most over-the-counter supplements contain D3, but many prescription forms of vitamin D deliver ergocalciferol. For example, Drisdol, a high-dose formulation of D (50,000 IU) designed for short-term weekly administration to rapidly restore D levels in seriously-deficient patients, is ergocalciferol. Frequently, hospitals stock mostly the D2 kind.

Why It Matters

A recent review (“The case against ergocalciferol (vitamin D2) as a vitamin supplement”) summarizes:

“Pharmacopoeias have officially regarded these two forms as equivalent and interchangeable, yet this presumption of equivalence is based on studies of rickets prevention in infants conducted 70 years ago.”

The authors argue: 

“The case that vitamin D2 should no longer be considered equivalent to vitamin D3 is based on differences in their efficacy at raising serum 25-hydroxyvitamin D, diminished binding of vitamin D2 metabolites to vitamin D binding protein in plasma, and a nonphysiologic metabolism and shorter shelf life of vitamin D2.”

Their verdict: “Vitamin D2, or ergocalciferol, should not be regarded as a nutrient suitable for supplementation or fortification.”

Even More Reason to Take D3

Now a new study provides additional justification for preferring D3. 

Researchers at the University of Surrey, UK, performed a meta-analysis of 11 previously published, randomized-controlled trials on vitamin D supplements, with a total of 655 participants.

They found that D2 supplementation actually lowered levels of body-ready vitamin D3. In many of the studies, the vitamin D3 levels were lower in people taking vitamin D2 than they were in control groups not taking any vitamin D supplements!

This is a never-before reported finding. Moreover, new research suggests D3 and D2 may have qualitatively different impacts on immunity. The D3 kind is said to uniquely stimulate the body’s interferon defense system, that provides a bulwark against bacterial and viral infections. 

With winter coming, and the threat of seasonal illnesses looming, it behooves health authorities to make sure that the millions of Americans at risk for vitamin D insufficiency have access to the reliable, preferred source—vitamin D3.

NTFactor® with Vitamin D3/K2 combines all the benefits of D3 with the cell-restoring power of patented NTFactor® phospholipid blend, in a tasty chewable vanilla wafer.