Mushrooms Have Vitamin D, and Multiple Forms of It

By Robby Gardner, Associate Editor

A team of Boston University researchers says that mushrooms, when exposed to ultraviolet (UV) light, are a plentiful human food source of vitamin D. Their conclusions, however, just published in the journal Dermato-Endocrinology, contradict some recent studies.

There's a debate over bioavailability of mushroom vitamin D, and it relates primarily to the form of vitamin D in mushrooms, called vitamin D₂ (ergocalciferol). Past studies conclude that this form isn’t as bioavailable to humans as animal-based vitamin D₃ (cholecalciferol), which is why most commercial dietary supplements contain the latter. Despite the argument, some mushroom farmers irradiate their product with UV to increase vitamin D levels. Mushrooms such as white button (Agaricus bisporus) contain negligible amounts of vitamin D when they grow in darkness; but, place them under UV light, and they become abundant vitamin D sources.

In a randomized, placebo-controlled trial, researchers assigned 30 adults to consume daily capsules containing 2000 IU of white button mushroom extract, vitamin D₂, or vitamin D₃ for three months during winter. The researchers measured blood samples for 25-hydroxyvitamin D, a most common marker for human vitamin D levels. At baseline and the end of the study, vitamin D levels were not statistically different in either group.

In jointly-published research, the Boston University team analyzed UV-exposed extracts of crimini, oyster, portabella, shiitake, white button mushrooms, and white button mushroom powder. They found that, beyond presence of vitamin D₂ precursors in all mushrooms, UV-exposed oyster, white botton, and shiitake also exhibited vitamin D₃ precursors. Shiitake even contained a precursor for vitamin D_4.

“It had always been assumed that UV irradiated mushrooms were only capable of producing vitamin D₂,” wrote the researchers. “Our study confirms that some mushrooms do contain provitamin D₄, and we now also report that shiitake mushrooms contain 7-DHC. Therefore, during UV irradiation, some mushrooms are capable of producing vitamin D₂, vitamin D₃, and vitamin D₄.”

Despite these findings, a nonprofit organization called The Vitamin D Council still encourages dietary supplementation with vitamin D3 over vitamin D2.

Monterey Mushrooms Inc. provided mushrooms for the study.