Eating mushrooms may be as effective at raising serum vitamin D levels as taking capsuled supplements, researchers reported here.

In a small randomized trial, 12 weeks of daily intake of mushroom extract raised serum 25-hydroxyvitamin D [25(OH)D] levels comparably to daily intake of vitamin D₂ or D₃ supplements, Michael Holick, MD, PhD, of Boston University, and colleagues reported at the joint American Society for Biochemistry and Molecular Biology and the Experimental Biology meeting in Boston.

"These results provide evidence that ingesting mushrooms that have been exposed to ultraviolet light and contain vitamin D2 are a good source of vitamin D that can improve the vitamin D status of healthy adults," Holick said in a statement.

Mushrooms produce vitamin D₂, or ergocalciferol, when exposed to sunlight or ultraviolet radiation, in a similar process by which humans produce vitamin D₃, or cholecalciferol. Not all plants possess this property, but fungi, seaweed, and yeast do.

Clinicians largely recommend vitamin D₃ supplements, particularly for those who are vitamin D deficient or insufficient, but studies have shown vitamin D₂ to be effective at increasing serum levels of the vitamin as well.

Kurt Kennel, MD, of the Mayo Clinic in Rochester, Minn., who was not involved in the study, noted that "vitamin D₂ has gotten a bit of a bad rap in the scientific literature in the last couple of years," but added that both forms of the vitamin have been shown to be beneficial for calcium and bone metabolism.

"We don't want to look at one or the other as ineffective," he told MedPage Today, "but there probably is a difference. We wouldn't want to say that this is an equivalent way of treating vitamin D deficiency."

However, he added, mushrooms are likely "a very reasonable approach for people who want to get vitamin D from foods that are not animal-based."

To determine whether eating mushrooms -- in this study, extract of dried white button mushrooms (Agaricus bisporus) -- was as effective at increasing and maintaining vitamin D status as supplemental vitamins D₂ or D₃, Holick and colleagues randomized 30 adults, mean age 35.2, to one of three interventions taken once a day for 12 weeks during the winter:

• Capsules containing 2,000 IU of vitamin D₃
• Capsules containing 2,000 IU of vitamin D₂
• 2,000 IU of mushroom powder containing vitamin D₂

Patients had similar baseline levels of serum vitamin D:

• D₃ group: 17.1 ng/mL
• D₂ group: 19.4 ng/mL
• Mushroom group: 20.9 ng/mL
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A total of 25 patients completed all 12 weeks of the study, and serum vitamin D levels gradually increased until they plateaued at about 7 weeks for all three groups and were maintained for the next 5 weeks, the researchers said.

At the end of the study, vitamin D levels among those eating mushrooms were comparable to those taking vitamin D supplements:

• D₃ group: 34.4 ng/mL
• D₂ group: 29.2 ng/mL
• Mushrooms: 31.1 ng/mL

Holick said the findings suggest that taking mushrooms and the vitamin D₂ they provide can improve serum vitamin D levels.

The results confirm other studies that have shown eating vitamin D₂ -- either in the form of fortified orange juice, a supplement, or a pharmaceutical formulation -- can increase total circulating serum 25(OH)D concentrations for at least 3 months and up to 6 years, Holick said.

He added that exposing mushrooms to UVB light can produce vitamins D₃ and D₄ as well, giving patients additional vitamin D.