Mushrooms make vitamin D the same way human skin does: a compound in their cell membranes reacts to ultraviolet (UV) light and converts into vitamin D. In mushrooms, that starting compound is called ergosterol, and UV exposure turns it into vitamin D2 (ergocalciferol). Mushrooms grown in the dark, which is how most store mushrooms are raised, contain only trace amounts of vitamin D unless they are deliberately exposed to UV light before or after harvest.
The Ergosterol-to-Vitamin-D2 Pathway
Ergosterol sits in the outer membrane of mushroom cells, concentrated in the cap and gills. When UV-B light hits ergosterol, it triggers a photochemical reaction that opens part of the molecule’s ring structure, forming previtamin D2. This previtamin D2 then rearranges through a temperature-dependent process into stable vitamin D2. The same basic chemistry happens in human skin, where UV light converts a cholesterol-related compound into vitamin D3 instead of D2.
Because this reaction depends entirely on UV exposure, the vitamin D content of any mushroom is not fixed. It depends on how much UV light the mushroom received, at what wavelength, for how long, and how the ergosterol was distributed in the tissue.
Why Most Grocery Store Mushrooms Are Low in Vitamin D
Commercial mushrooms are typically grown indoors under fluorescent lighting that produces little to no UV radiation. That growing method keeps costs low and yields consistent, but it also means these mushrooms build up very little vitamin D2 despite containing plenty of ergosterol, the raw material. A serving of untreated white button mushrooms generally supplies only a small fraction of daily vitamin D needs.
Some growers now expose mushrooms to UV-B light or natural sunlight for a short period, often just before or during harvest, specifically to raise vitamin D2 content. Packages treated this way are usually labeled “UV-treated,” “vitamin D mushrooms,” or “high in vitamin D,” and the difference in content compared to untreated mushrooms can be substantial.
How Much Vitamin D Do Mushrooms Actually Have?
Vitamin D content varies widely by species, UV dose, and treatment method, so any single number is only an estimate. Research on white button mushrooms (Agaricus bisporus) offers the most consistent picture:
- Untreated white button mushrooms (100 g): Roughly 20–40 IU (0.5–1 mcg). Grown without meaningful UV exposure.
- UV-treated white button mushrooms (100 g): Can exceed 400 IU (10 mcg). Level depends on UV dose and tends to remain above this threshold through typical storage if consumed before the best-before date.
- UV-exposed Agaricus bisporus (75 g serving): Can exceed 100% of the daily recommendation, based on an 18 mcg yield reported in dietary modeling research.
- Fatty fish, such as salmon (100 g): Roughly 400–1,000+ IU (10–25+ mcg), depending on species and whether wild-caught or farmed.
- Fortified milk (1 cup): Roughly 100 IU (2.5 mcg), depending on the fortification level set by the manufacturer.
For an exact figure on a specific product, check the Nutrition Facts label or look up the item in the USDA FoodData Central database, since values differ by brand and growing method.
Vitamin D2 vs. Vitamin D3: What’s the Difference?
Vitamin D2 and D3 are both forms of vitamin D, but they come from different sources and are processed slightly differently by the body.
- Vitamin D2 (ergocalciferol): Made by mushrooms, yeast, and some UV-treated foods. This is the form found in UV-exposed mushrooms.
- Vitamin D3 (cholecalciferol): Made by human skin from sun exposure and found in animal foods like fatty fish, egg yolks, and fortified dairy. It is also the most common form in supplements.
Both forms raise blood vitamin D levels, and the body converts each into the same active hormone, calcitriol. Some research has found that vitamin D3 may be somewhat more effective at raising and maintaining blood vitamin D levels over time compared to equal doses of D2, though findings across studies are mixed and the practical difference for someone eating mushrooms as part of a varied diet is generally considered small. Mushrooms remain the only significant non-animal, unfortified food source of vitamin D, which makes UV-treated mushrooms a notable option for people following vegan or vegetarian diets.
What Does the Human Evidence Show?
A 2018 scientific review in the journal Nutrients examined the existing research on mushrooms as a dietary vitamin D source. It found that vitamin D2 from UV-exposed mushrooms is absorbed and used by the body, and that human intervention studies have shown increases in blood vitamin D levels after regular consumption of UV-treated mushrooms. The review also reported that vitamin D2 in UV-exposed mushrooms holds up reasonably well during typical cooking and storage, staying above meaningful levels through the product’s shelf life in most cases studied.
A 2024 dietary modeling study published in Frontiers in Nutrition estimated that eating UV-exposed button mushrooms about four times a week could help most adults meet vitamin D recommendations, and cited prior research showing that UV-exposed mushrooms increased vitamin D status in people who started out deficient.
These findings come from a mix of controlled human feeding studies and food composition analysis, which is stronger evidence than laboratory or animal-only research. Still, the number of large, long-term human trials specifically on mushroom-derived vitamin D2 remains limited compared to the research base on vitamin D3 from supplements or sun exposure.
Extra-Caution Groups
Talk with a qualified clinician before making mushrooms or any food a significant part of a vitamin D strategy if any of these apply:
- You have kidney disease, sarcoidosis, or a history of hypercalcemia, since these conditions can affect how your body handles vitamin D and calcium.
- You take medications that interact with vitamin D metabolism, including certain diuretics, corticosteroids, or seizure medications.
- You are pregnant, breastfeeding, or considering a change in your child’s diet.
- You have a diagnosed vitamin D deficiency and are relying on food alone instead of following your clinician’s treatment plan.
This article does not diagnose vitamin D deficiency or recommend a specific intake, dose, or supplement. A blood test is the only reliable way to know your vitamin D status.
How to Get Vitamin D From Mushrooms: A Quick Checklist
- Check the package for “UV-treated,” “vitamin D mushrooms,” or a specific vitamin D amount on the Nutrition Facts panel.
- Do not assume all mushrooms have meaningful vitamin D. Untreated mushrooms grown in the dark generally do not.
- Store and use mushrooms before the best-before date, since vitamin D2 content can decline over time.
- Remember that food alone may not close a significant vitamin D gap. Ask a clinician about testing if you suspect deficiency.
- Treat mushrooms as one possible piece of a broader vitamin D strategy that may include sun exposure, other foods, or supplements under medical guidance, not a replacement for medical advice.
Frequently Asked Questions
Do all mushrooms have vitamin D?
No. All mushrooms contain ergosterol, the compound that can become vitamin D2, but only mushrooms exposed to meaningful UV light actually convert much of it. Mushrooms grown entirely in the dark have very little vitamin D.
Can I put regular grocery store mushrooms in sunlight to boost vitamin D at home?
Placing mushrooms gill-side up in direct sunlight for a period of time can increase their vitamin D2 content, based on the same UV-conversion process studied in commercial UV treatment. Research on precise home conditions, exposure times, and resulting vitamin D levels is limited, so the exact increase you would get at home is hard to predict.
Is mushroom vitamin D2 as good as vitamin D3 from fish or supplements?
Both forms raise blood vitamin D levels and convert to the same active form in the body. Some evidence suggests D3 may be somewhat more effective at maintaining vitamin D status long-term, but D2 from UV-treated mushrooms has been shown in human studies to meaningfully raise vitamin D levels.
How can I tell if the mushrooms I bought were UV-treated?
Check the package label for terms like “UV-treated,” “vitamin D mushrooms,” or “grown with UV light,” and check the Nutrition Facts panel for the vitamin D amount. If nothing is listed, the mushrooms were most likely grown without significant UV exposure.
Evidence Limits
Most of the human research on mushroom-derived vitamin D2 comes from a relatively small number of controlled feeding studies and food composition analyses, largely focused on white button mushrooms. Less data exists on other commonly eaten species. Findings on how D2 compares to D3 for long-term health outcomes, rather than short-term blood level changes, are still developing. This article reflects the evidence available as of publication and will be updated if the research changes.
Educational Disclaimer
This article is for general educational purposes only and is not medical advice. It does not diagnose any condition or recommend a specific dose, supplement, or treatment. Vitamin D needs vary by individual health history, medications, and lab results. Talk with a qualified clinician before changing your diet or supplement routine, especially if you have a health condition, take medication, or are pregnant or breastfeeding.
Related reading on Mushroom Health Benefits: see how claims on this site are rated in our evidence grading and source policy, and review the full scope of our medical disclaimer before applying any information to your personal health decisions.