Understanding Vitamin D in Mushrooms
Unlike most plant-based foods, mushrooms are a unique non-animal source of vitamin D. They contain a substance called ergosterol, a precursor that is converted into vitamin D2 (ergocalciferol) when exposed to ultraviolet (UV) radiation, much like human skin produces vitamin D3 from sunlight. The level of vitamin D in a mushroom is directly proportional to its exposure to UV light, whether from natural sunlight or artificial UV lamps. Therefore, the simple answer to which mushroom has the most vitamin D is any mushroom that has received significant UV exposure. This is why wild varieties and commercially irradiated mushrooms are far superior to standard, dark-grown cultivated versions.
The Top Contenders for Vitamin D
Several mushroom species stand out for their vitamin D content, but their potency is heavily influenced by how they are grown and processed. Here are the leading types:
Wild Mushrooms
Wild mushrooms are naturally high in vitamin D because they grow outdoors in sunlight. The levels can vary significantly based on growing conditions, sun exposure, and harvesting time. The most notable species include:
- Porcini (Boletus edulis): Considered one of the highest natural sources, with wild varieties reporting up to 58.7 µg (2348 IU) of vitamin D per 100g.
- Chanterelle (Cantharellus spp.): Wild chanterelles are also excellent sources, providing up to 29.8 µg (1192 IU) per 100g.
- Morel (Morchella spp.): Like other wild fungi, morels can contain significant vitamin D, with one study finding over 5 µg (204 IU) per 100g.
UV-Treated Commercial Mushrooms
To provide a consistent, high-vitamin D product, some commercial growers intentionally expose their harvested mushrooms to UV lamps. This process is highly effective and creates predictable, concentrated levels of vitamin D.
- Maitake (Grifola frondosa): Some producers use proprietary UV methods to boost maitake mushrooms, with samples ranging from 0.1 µg to as high as 56 µg (2242 IU) per 100g.
- White Button & Cremini (Agaricus bisporus): Although normally very low in vitamin D when grown in the dark, UV-treated versions can deliver significant amounts. Some UV-exposed cremini can contain over 1086 IU per serving, while UV-treated portabellas can reach over 750 IU.
- Lung Oyster (Pleurotus pulmonarius): In a study, lung oyster mushrooms showed exceptionally high natural vitamin D2 levels (15.88 µg per 100g EP) and maintained good levels even after cooking.
The Low-Down on Untreated Mushrooms
Most mushrooms found in typical grocery stores are cultivated in dark, controlled environments and, as a result, contain very little or no vitamin D. This includes the standard white button, cremini, portabella, and shiitake varieties unless they are explicitly labeled as "UV-treated" or "high in vitamin D." For example, the USDA notes that non-UV-treated retail mushrooms contain negligible amounts, often less than 1 µg per 100g.
How to Increase Vitamin D in Your Own Mushrooms
If you buy regular, untreated mushrooms, you can easily boost their vitamin D content at home. The process is simple and requires only sunlight.
Here are the steps:
- Slice the mushrooms: This increases the surface area exposed to UV light.
- Place them gill-side up: The gills contain a higher concentration of ergosterol, so exposing them directly to the light maximizes conversion.
- Lay them on a tray: Arrange the mushrooms in a single layer on a plate or tray.
- Expose to midday sun: Place the tray in direct sunlight around midday for at least 15 to 120 minutes. The amount of vitamin D generated will depend on factors like sun intensity, time of year, and latitude.
- Cook and consume: Use the sun-enriched mushrooms in your recipes. Cooking can cause some vitamin D loss, especially when boiling, but a significant portion will be retained.
Comparison of Vitamin D in Mushrooms
| Mushroom Type | Growing Conditions | Typical Vitamin D (per 100g) | Notes |
|---|---|---|---|
| Wild Porcini | Natural sunlight | High (~58.7 µg) | Found in forests, can vary based on sun exposure. |
| Wild Chanterelle | Natural sunlight | High (~21.1 µg) | Also a great natural source. |
| UV-Treated Maitake | Cultivated, then UV-treated | Very High (up to 56 µg) | Specific commercial products. |
| UV-Treated Button/Cremini | Cultivated, then UV-treated | High (>10 µg) | Widely available commercially treated options. |
| Home-Sunned Button | Dark-grown, then sun-exposed | High (over 10 µg) | Can be done easily at home. |
| Untreated Store-Bought | Grown in darkness | Negligible (<1 µg) | Most common type found in supermarkets. |
Conclusion
The mushroom that has the most vitamin D is almost always a UV-exposed one, whether it gained its dose naturally in the wild or through a commercial or at-home treatment process. For those seeking a high and reliable source, commercially UV-treated mushrooms are an excellent option and widely available. If you prefer to enhance your own, simply placing regular cultivated mushrooms in the sun for an hour can dramatically increase their vitamin D content. This makes mushrooms a uniquely flexible food for boosting dietary vitamin D, especially for those on a vegetarian or vegan diet.
Can you overdose on vitamin D from mushrooms?
It is extremely unlikely to overdose on vitamin D from consuming mushrooms. For healthy adults, consuming vitamin D-enriched mushrooms is considered safe, and mushrooms do not produce excessive levels that would be toxic.
Where to find UV-treated mushrooms
UV-treated mushrooms are increasingly common in supermarkets. Look for labeling that specifically states they are "UV-treated" or "rich in vitamin D".
Bioavailability of Mushroom Vitamin D
Studies have shown that vitamin D2 from UV-irradiated mushrooms is bioavailable and effective in raising and maintaining healthy vitamin D levels in adults. Some research suggests vitamin D3 from animal sources may be slightly more effective, but mushroom D2 is still a valuable source, especially for vegans and vegetarians.
