Mushrooms really do make vitamin D when ultraviolet light hits them, and the food-science story usually stops there. The clinical story does not. In a 2026 randomised trial, adults eating 800 IU a day of UV-exposed mushrooms through a Northern winter did raise their vitamin D2 — and their vitamin D3 fell further than the control group's, leaving total vitamin D status no better. Two-thirds of the mushrooms bought for that trial contained any D2 at all.
Mushrooms grown in the dark contain almost no vitamin D but are rich in ergosterol, which ultraviolet light converts to vitamin D2 (ergocalciferol). A UV-B dose of 1.5 J/cm² raised button mushroom content from under 1 to 491 µg per 100 g in one study, and that D2 is absorbed as well as a D2 supplement. The complication is displacement: a meta-analysis of six trials found UV mushrooms raised 25(OH)D2 by 24.2 nmol/L while lowering 25(OH)D3 by 12.6 nmol/L, with a significant net gain only in people who started deficient. A 2026 trial in overweight adults found the D3 decline outpaced the D2 rise, so total 25(OH)D did not improve — and only 67% of the supposedly UV-exposed mushrooms actually contained vitamin D2.
Mushrooms are still the only meaningful non-animal food source of vitamin D, which matters a great deal to some diets. It is just a more conditional benefit than the headline suggests.
Why Mushrooms Can Make Vitamin D at All
Because of ergosterol. It sits in fungal cell membranes the way cholesterol sits in ours, and ultraviolet-B light converts it to vitamin D2 in exactly the same photochemical way UV-B converts 7-dehydrocholesterol in skin to vitamin D3.
This is why the growing conditions decide everything. Commercially cultivated mushrooms are raised in dark, climate-controlled rooms and contain essentially none. The same species given a few minutes of UV exposure — or a wild mushroom that grew in daylight — can contain a great deal.
The conversion is fast and the numbers are large. Urbain's trial irradiated fresh button mushrooms at 1.5 J/cm² and lifted vitamin D2 from below 1 to 491 µg per 100 g, roughly 19,600 IU.
Which Species Actually Have It?
Wild-grown species are the ones with meaningful natural content, because they grew under the sky. Chanterelles and morels are the two usually cited in European food composition tables; cultivated shiitake, oyster and button mushrooms have negligible amounts unless treated.
Drying in sunlight adds more, which is the traditional practice behind the shiitake numbers — our shiitake and vitamin D2 article covers how gill exposure and drying method change the figure.
What no species gives you is a predictable dose. The same chanterelle picked from shade or from an open clearing differs, and a dried mushroom that spent its drying days indoors differs again. This is a food, not a tablet, and the variance is genuinely large.
Is Mushroom D2 Absorbed?
Yes, and this part of the evidence is clean. Urbain's five-week randomised trial gave 26 vitamin-D-deficient young adults 28,000 IU of vitamin D2 per week either through a soup made from UV-irradiated mushrooms or through a D2 supplement, against placebo, during winter.
Serum 25-hydroxyvitamin D rose significantly in the mushroom group against placebo by two weeks, and the weekly rise in the mushroom arm (3.9 nmol/L) was statistically indistinguishable from the supplement arm (4.7 nmol/L). The vitamin D2 in a mushroom behaves like the vitamin D2 in a capsule.
Which means the interesting question is not absorption. It is what vitamin D2 does once it is in you.
The Displacement Problem
Vitamin D2 and vitamin D3 compete. Cashman's 2016 meta-analysis pooled six randomised trials of UV-exposed mushrooms and found that serum 25(OH)D2 rose by 24.2 nmol/L — while serum 25(OH)D3 fell by 12.6 nmol/L over the same period.
About half the gain is therefore cancelled internally. The mechanism is thought to involve competition for the vitamin D binding protein and for the enzymes that hydroxylate and clear both forms, and the practical consequence is that mushroom D2 is not additive with the D3 you already have.
The pooled effect on total 25(OH)D across all six trials was not significant. Split by baseline, the picture sharpens: the three European trials, whose participants averaged 38.6 nmol/L at baseline — deficient — showed a significant gain of 15.2 nmol/L. The three US trials, averaging 81.5 nmol/L — replete — showed nothing at all (P = 0.83).
That is the rule worth taking away. UV mushrooms help people who are short of vitamin D and do approximately nothing for people who are not.
What the 2026 Trial Found
Worse than nothing, in one population. Comboni's team randomised 41 adults classified as overweight or class I obese to eat 84 g of fresh Agaricus bisporus twice daily — produced to contain 400 IU of vitamin D2 per serving, 800 IU a day — or breadcrumbs, through late autumn and winter, for six weeks.
Serum 25(OH)D2 rose in the mushroom group as expected. Serum 25(OH)D3 declined more steeply than in the control group, and total 25(OH)D fell in both groups with no difference between them. The mushrooms did not offset the seasonal decline they were tested against.
Then the supply-chain finding, which the authors flag as unexpected: weekly assay of the purchased mushrooms showed that only 67% of them contained any vitamin D2. One third of a batch sold as UV-exposed delivered none.
Species and Practical Content
| Source | Typical vitamin D status | Why |
|---|---|---|
| Cultivated button, oyster, shiitake (indoor) | Negligible | Grown in darkness; ergosterol never irradiated |
| UV-treated cultivated mushrooms | Potentially very high | Up to 491 µg/100 g demonstrated; batch reliability poor |
| Wild chanterelle, morel | Modest and variable | Grew in daylight; depends on canopy and exposure |
| Sun-dried mushrooms | Raised, unpredictably | Conversion continues during drying if UV reaches the gills |
| Mushroom extract capsules | Effectively none | Extraction targets glucans; vitamin D is not assayed or claimed |
Does This Matter for Supplements?
Barely, and that is worth stating plainly. Mushroom extract capsules are manufactured for beta-glucans, no manufacturer assays vitamin D in them, and nothing in the extraction process is designed to retain it. If you are buying mushroom capsules for vitamin D, you are buying the wrong product.
The vitamin D conversation belongs to whole mushrooms, and specifically to how they were grown and dried. That is a food purchase and a cooking decision, not a supplement one — which is also true of ergothioneine, the other nutrient mushrooms are uniquely good for.
What to Actually Do
- If you are deficient, UV mushrooms are a legitimate source. That is the population where the meta-analysis found a real 15.2 nmol/L gain.
- If your vitamin D is already adequate, do not count on them. The replete trials found no effect, and the D2 you add can lower the D3 you have.
- Do not treat a "UV-exposed" label as a dose. A third of one trial's purchased batch contained no vitamin D2 whatsoever.
- Prefer wild-grown and sun-dried species if you want it from food. Chanterelles and morels grew in daylight; indoor cultivated mushrooms did not — see our drying guide.
- Do not buy mushroom extracts for vitamin D. They are made for beta-glucans and no vitamin D figure is assayed or claimed.
- Test rather than guess. Because the benefit depends entirely on your starting level, a 25(OH)D measurement is what decides whether any of this is worth doing.
The Honest Summary
Mushrooms are the only significant plant-kingdom source of vitamin D and the biochemistry behind that is elegant and real. The absorption evidence is solid: mushroom D2 works as well as supplement D2.
What the trials add is a condition and a warning. The condition is baseline — the benefit is concentrated almost entirely in people who are already deficient, and disappears in people who are not. The warning is displacement: adding D2 measurably lowers D3, which is why a 2026 trial at 800 IU a day through winter could raise one form and still leave total vitamin D status unchanged. For a vegan or vegetarian diet short of vitamin D in winter, mushrooms remain genuinely useful. For everyone else, they are a good food with an overstated nutritional headline.
Frequently Asked Questions
Do mushrooms contain vitamin D?
Only if ultraviolet light reached them. Mushrooms are rich in ergosterol, which UV-B converts to vitamin D2, so indoor-cultivated mushrooms contain almost none while UV-treated, wild-grown or sun-dried ones can contain a great deal.
Is mushroom vitamin D2 as good as vitamin D3?
It is absorbed as well, but it does not add cleanly. A meta-analysis of six trials found UV mushrooms raised 25(OH)D2 by 24.2 nmol/L while lowering 25(OH)D3 by 12.6 nmol/L, so roughly half the gain is cancelled internally.
How many mushrooms would I need to eat?
In the 2026 trial, 168 g of fresh UV mushrooms a day was intended to supply 800 IU of vitamin D2 — and still did not prevent the winter decline in total vitamin D. Untreated cultivated mushrooms supply essentially none at any quantity.
Can I make my own vitamin D mushrooms in sunlight?
The photochemistry works — gills facing the sun convert ergosterol to D2 — but you cannot know the result. Latitude, season, cloud, glass and duration all change it, and unlike the irradiation studies you have no way to measure what you produced.
Do mushroom supplements contain vitamin D?
Not meaningfully. Extracts are manufactured and standardised for beta-glucans, no vitamin D content is assayed or claimed, and nothing in the process is designed to preserve it.
Shop Whole Mushrooms
Vitamin D is a whole-mushroom question, so this is a food purchase. Dried chanterelle (100 g €39, 500 g €139) and dried morels (100 g €39, 1 kg €299) are wild-harvested species that grew in daylight. Dried shiitake (50 g €39, 100 g €69) is the species with the longest tradition of sun-drying behind it. Browse Gourmet & Forest Mushrooms. Free shipping on orders over €50.
Related Articles
- Shiitake and Vitamin D2: Drying and UV
- Ergothioneine: The Antioxidant You Cannot Make
- Morel Mushroom Nutritional Profile
- Chanterelle Mineral Content
- How to Cook and Dry Chanterelles
- Chanterelles for Eye Health
- How to Store Mushroom Extracts and Powders
Sources
- Cashman KD, Kiely M, Seamans KM, Urbain P. Effect of ultraviolet light-exposed mushrooms on vitamin D status: liquid chromatography-tandem mass spectrometry reanalysis of biobanked sera from a randomized controlled trial and a systematic review plus meta-analysis. J Nutr. 2016;146(3):565-575. PubMed 26865648
- 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;65(8):965-971. PubMed 21540874
- Comboni LM, Glover ES, Napolitano SC, et al. Does consuming fresh ultraviolet light-exposed mushrooms offset the seasonal decline in serum total 25OHD in adults classified as overweight and class I obese? Results from a randomized controlled trial. Foods. 2026;15(9):1572. PubMed 42121515
- Kalaras MD, Richie JP, Calcagnotto A, Beelman RB. Mushrooms: a rich source of the antioxidants ergothioneine and glutathione. Food Chem. 2017;233:429-433. PubMed 28530594
- Ba DM, Gao X, Al-Shaar L, et al. Prospective study of dietary mushroom intake and risk of mortality: results from continuous National Health and Nutrition Examination Survey (NHANES) 2003-2014 and a meta-analysis. Nutr J. 2021;20(1):80. PubMed 34548082