mushrooms produce vitamin D3 Whether or not mushrooms provide a legitimate source of vitamin D activity has been a hotly contested topic over the past few years. Back in 2014, we were pulled into the fray after publishing the mycologist Paul Stamet's article on the topic titled, "Place Mushrooms in Sunlight to Get Your Vitamin D." Soon after, the Healthy Home Economist published an article by Sylvia P. Onusic aggressively titled "Debunking the Absurd Notion of Vitamin D in Mushrooms," wherein she calls out the presumably erroneous view of Paul that non-animal sources of vitamin D are relevant to meeting nutritional requirements for these indispensable biomolecules. Sylvia states:

"In the past few years many blogs have expounded on the "glorious" vitamin D properties of mushrooms.

"Mushrooms are not only wonderful sources of vitamin D, but they offer us many opportunities for maintaining and improving health," says mycologist Paul Stamets.

But that wonderful source he's talking about is vitamin D2, which is otherwise made artificially from radiating ergot and yeasts."

In her article, Sylvia points out important differences between D2 and D3, but argues so strongly for the superiority of vitamin D3 over D2 that it would seem to imply vegans or vegetarians who do not have sufficient sun exposure should reconsider their dietary/ethical stance or suffer dire health consequences.

What I find so interesting about this exchange is that Paul never argues that sun-exposed mushrooms are superior to animal derived forms of vitamin D3; nor is he denying that vitamin D3 is superior in bioactivity to vitamin D2. He is only arguing that mushrooms are a legitimate alternative, and considering the needs of sunlight-deprived vegans/vegetarians or those who are not in a position to access or manufacturer animal derived vitamin D3 themselves, they may be the only available source to them.

Decomposing The Assumption That Mushrooms Can't Produce Vitamin D3
Research exists from 2013 that demonstrates how sunlight-exposed mushrooms produce not only D2, but also D4 (with about 60% the biological activity of D3)[1] and D3 itself – a discovery that fundamentally undermines Sylvia's argument against mushrooms.

Published back in 2013 in the journal Dermatoendocrinology and titled, "Photobiology of vitamin D in mushrooms and its bioavailability in humans," the study revealed that mushrooms indeed are a vegan source of vitamin D3 and related isomers:

"Shiitake mushrooms not only produce vitamin D2 but also produce vitamin D3 and vitamin D4."

The study also referenced research that disproves Sylvia's claims:

"A study of the bioavailability of vitamin D2 in mushrooms compared with the bioavailability of vitamin D2 or vitamin D3 in a supplement revealed that ingestion of 2000 IUs of vitaminD2 in mushrooms is as effective as ingesting 2000 IUs of vitamin D2 or vitamin D3 in a supplement in raising and maintaining blood levels of 25-hydroxyvitamin D which is a marker for a person's vitamin D status." [Note: Full study details at the end of this article]

Their conclusion clearly indicates that mushrooms constitute an excellent source of vitamin D:

"Therefore, mushrooms are a rich source of vitamin D2 that when consumed can increase and maintain blood levels of 25-hydroxyvitamin D in a healthy range. Ingestion of mushrooms may also provide the consumer with a source of vitamin D3 and vitamin D4."

Clearly, if vitamin D3 can be produced by fungi, the ongoing argument between those who believe that animal products are necessary to fulfill basic human dietary requirements and those who maintain that the vegan/vegetarian lifestyle is rendered more complex than hitherto considered. We have also recently seen other basic assumptions about human physiology and metabolic nees challenged. For instance, the discovery that chlorophyll is capable of helping the body capture energy directly from the sun, a capability formerly attributed only to autotrophs like plants. We have also seen turmeric's role in helping vegetarian's enhance DHA synthesis, perhaps undermining the Paleolithic fixation on eating much higher on the trophic scale for optimal health. There is also the fact that since we are constituted by 99% microbes, everything we once believed about our body and it's relationship to the world has basically been redefined.