Mushrooms and Vitamin D Content

mushrooms vitamin D levels boosted with sunlight

Many mushrooms contain vitamin D2

Vitamin D from mushrooms? By now most of us should know that mushrooms provide one of the few ways to naturally supplement vitamin D – outside of some healthy sunshine.

Yet mushrooms to supply some vitamin D

However, the unfortunate fact is that most culinary mushrooms provide only small amounts of vitamin D by themselves. Most less than 100 IU per gram. Furthermore, there is the question of whether D2 – primarily produced by mushrooms – is therapeutic.

But did you know that you can significantly turn up the vitamin D2 dial on practically every type of mushroom with a simple step?

Sun exposure heightens vitamin D levels

Recent research has firmly established that placing most mushrooms – after they are picked and even dried – into the sun or another source of UV-B radiation will dramatically increase their vitamin D levels.

In one study, USDA researchers analyzed vitamin D content among a variety of mushrooms both in normal conditions – without drying in the sun – and after drying or otherwise exposing the mushrooms to natural sunlight after their harvest.

For example, Maitake mushrooms tested from one supplier had little vitamin D, while Maitake from another producer who exposed them to sunlight contained a high of 2529 IU per 100 grams. Other Maitakes from producers who exposed their mushrooms to sunlight contained 1416 IU of vitamin D.

The vitamin D2 levels of even white button mushrooms can be spiked with sunlight. While normally-grown button mushrooms may contain only a few IU, a little sunlight will change that. One test compared both sunlight exposure and UVB lamp exposure using Buttons mushrooms. A short exposure to sunlight increased the vitamin D levels from 5 IU to 374 IU per 100 grams. Meanwhile a short exposure to a UV-B lamp increased the same mushrooms from 5 to 410 IU per 100 grams.

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It doesn’t matter that the mushrooms haven’t been exposed to sunlight by the producer. We can still boost their vitamin D2 levels at home. Just a few minutes in the sun can dramatically boost their levels. Pointing their gills upward can increase these levels even more.

These can even get to astronomical levels if they are put in the sun long enough. Paul Stamets and his team put Shiitake mushrooms with 40 IU of vitamin D into the sunlight for eight hours with the gills upward. The resulting analysis revealed an incredible 46,000 IU of vitamin D2. Another six hours (14 hours in total) of sunlight exposure kicked up their levels to an eye-boggling 267,000 IU of vitamin D per 100 grams.

As mentioned, the vitamin D produced by mushrooms is primarily D2 – ergocalciferol – but they also produce conservative amounts of vitamin D3 – cholecalciferol – and vitamin D4 – 22,23-dihydroergosterol. While vitamin D2 is also used by the body in place of the vitamin D3 produced by the sun, it should be noted that D3 is the healthiest and most active form of vitamin D in the body. Vitamin D4 is most known for increasing blood calcium levels, though it is not considered a replacement for D3. Outside of mushrooms, there are few natural sources of D4.

The dramatically boosted vitamin D levels from mushrooms are primarily D2.

Is this vitamin D2 therapeutic?

Recent research has brought this into question, as researchers have reviewed studies on D2 supplementation. Realnatural will discuss these in a later article.

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But more specific to mushrooms’ D2 is a recent study conducted at the University of California at Davis.

For six weeks the UC researchers gave 38 adult human volunteers mushrooms not treated with UV exposure (containing 34 IU of D2 per 100 grams), UV-treated mushrooms (containing from 352 to 684 IU D2 per 100 grams), or a supplement containing 1000 IU of D2 together with untreated mushrooms. Before and after, the researchers tested the subjects’ blood levels of vitamin D2 and D3 (25(OH)D2 and 25(OH)D3). This measured their relative vitamin D status.

The researchers did find that the subjects’ vitamin D2 (25(OH)D2) levels went up. But their vitamin D3 (25OHD3) levels went down about the same, netting no increase in total vitamin D. Other research has shown that vitamin D supplements are not that therapeutic.And vitamin D supplements for children boost allergy risk.

Other research – which again we’ll cover later – has shown that vitamin D3 produced by the body in the presence of UVB sunlight exposure – is a much more therapeutic form of vitamin D, and that D2’s efficacy is questionable.

Yes, research does show that vitamin D2 from mushrooms can boost the body’s blood (25(OH)) levels. Research from Germany’s Freiburg University indeed confirmed that eating vitamin D-containing mushrooms boosted 25OHD levels in vitamin D-deficient people. But is this form of vitamin D truly therapeutic? We’ll cover this shortly.

Healthy Sun by Case Adams Naturopath

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Haytowitz DB. Vitamin D in Mushrooms. Nutrient Data Laboratory, Beltsville Human Nutrition Research Center, Belsville MD. USDA-ARS.

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Phillips KM, Horst RL, Koszewski NJ, Simon RR. Vitamin D4 in mushrooms. PLoS One. 2012;7(8):e40702. doi: 10.1371/journal.pone.0040702.

Simon RR, Phillips KM, Horst RL, Munro IC. Vitamin D mushrooms: comparison of the composition of button mushrooms (Agaricus bisporus) treated postharvest with UVB light or sunlight. J Agric Food Chem. 2011 Aug 24;59(16):8724-32. doi: 10.1021/jf201255b.

Urbain P, Singler F, Ihorst G, Biesalski HK, Bertz H. Bioavailability of vitamin D₂ from UV-B-irradiated button mushrooms in healthy adults deficient in serum 25-hydroxyvitamin D: a randomized controlled trial. Eur J Clin Nutr. 2011 Aug;65(8):965-71. doi: 10.1038/ejcn.2011.53.

Stamets P. Place Mushrooms in Sunlight to Get Your Vitamin D. Huffington Post. July 12, 2012.

Stephensen CB, Zerofsky M, Burnett DJ, Lin YP, Hammock BD, Hall LM, McHugh T. Ergocalciferol from mushrooms or supplements consumed with a standard meal increases 25-hydroxyergocalciferol but decreases 25-hydroxycholecalciferol in the serum of healthy adults. J Nutr. 2012 Jul;142(7):1246-52. doi:10.3945/jn.112.159764.


  • Case Adams, Naturopath

    California Naturopath, Ph.D. in Natural Health Sciences, Doctorate in Integrative Health Sciences, Board Certified Alternative Medicine Practitioner. Diplomas in Blood Chemistry, Clinical Nutritional Counseling, Homeopathy, Aromatherapy, Colon Hydrotherapy, certificates in Pain Management and Case Management/Contact Tracing. Has authored more than 30 books and hundreds of periodical articles on natural medicine. Recreational activities include surfing, sailing, running, biking, swimming, SUPing, hiking. Contact: case(at)caseadams(dot)com.

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