The Primary Natural Source: Mushrooms
Mushrooms are the most notable natural, non-animal source of vitamin D2. They synthesize this vital nutrient from a precursor compound called ergosterol when exposed to ultraviolet (UV) light. Most commercially grown mushrooms, cultivated in darkness, contain very little vitamin D2 unless they are specifically treated with UV light. However, wild mushrooms and those intentionally exposed to UV radiation can contain significant, nutritionally relevant amounts.
Types of UV-Enhanced Mushrooms
- White Button Mushrooms: When exposed to a UV light source, these common mushrooms can convert their ergosterol to vitamin D2. Commercially treated varieties are available, and the USDA reports significant vitamin D2 content in UV-treated portabella and maitake varieties as well.
- Shiitake Mushrooms: Both fresh and dried shiitake mushrooms can be a good source of vitamin D2 if exposed to UV light. The gills, which have a high concentration of ergosterol, are particularly effective at converting UV rays.
- Maitake Mushrooms: Certain proprietary growing methods use UV light to dramatically boost the vitamin D2 content in maitake mushrooms, yielding potent results.
How to Boost Mushroom Vitamin D2 at Home
You can increase the vitamin D2 content of mushrooms at home by exposing them to sunlight. Simply place store-bought, raw mushrooms (sliced side up is most effective) in direct sunlight for 15 minutes to an hour. A single serving can provide a substantial portion of the daily recommended intake. Store them in the refrigerator afterward; studies show the vitamin D2 content is relatively stable for about a week.
The Role of Fortified Plant-Based Products
For those on a plant-based diet, fortified foods are an accessible and reliable source of vitamin D2. These are products that have been artificially supplemented with the vitamin.
Commonly fortified plant products include:
- Plant Milks: Soy, almond, oat, and rice milks are often fortified with vitamin D2, offering a consistent dose in a common beverage.
- Cereals: Many breakfast cereals are enriched with a variety of vitamins, including D2.
- Orange Juice: Select brands of orange juice are fortified to provide a dose of vitamin D, along with their natural vitamin C.
- Tofu and Yogurt: Some varieties of plant-based tofu and yogurt are also fortified to increase their nutritional profile.
Other Plant Sources and Algae
Beyond mushrooms and fortified products, other plant-based sources of vitamin D2 are less common and typically provide only minimal amounts. Microalgae, however, can be a source.
- Microalgae (e.g., Chlorella): Certain microalgae contain provitamin D2 and can produce the vitamin upon UV exposure, much like fungi. Some commercially available Chlorella supplements have been found to contain both vitamin D2 and ergosterol.
- Native Plants: Research has found small, though often nutritionally insignificant, amounts of vitamin D2 in certain native plants, such as lemon myrtle leaves and Tasmanian mountain pepper.
Vitamin D2 vs. D3: A Quick Comparison
While both vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol) help with calcium absorption and bone health, they have different origins and slight differences in how they affect the body.
Comparison Table: Vitamin D2 vs. D3
| Feature | Vitamin D2 (Ergocalciferol) | Vitamin D3 (Cholecalciferol) |
|---|---|---|
| Primary Source | Fungi (mushrooms), UV-irradiated yeast, some algae, fortified plant foods | Animals (fatty fish, egg yolks), human skin's synthesis from sunlight, lichen (plant-based D3) |
| Absorption/Efficacy | Effective at raising vitamin D blood levels, though potentially less so than D3 over time. Bioavailability from mushrooms is well-documented. | Considered by some studies to be more effective at raising and maintaining vitamin D levels. |
| Suitability for Vegans | Ideal for vegans and vegetarians as it is primarily plant-derived. | Typically not suitable for vegans, with the exception of lichen-derived supplements. |
Cooking and Storage Considerations
Even with UV-enhanced mushrooms, proper preparation and storage are important to preserve vitamin D2 content. Studies show that vitamin D2 content is relatively stable during typical cooking methods, though retention rates vary. Pan-frying without oil, for example, shows high retention, while boiling can cause some loss. Storing UV-exposed mushrooms in the refrigerator for up to a week does not significantly reduce their vitamin D2 content.
Conclusion: Making the Right Plant-Based Choices
While the list of naturally occurring plants with substantial vitamin D2 is short, mushrooms offer a powerful and natural solution, particularly when exposed to UV light. Combined with the widespread availability of fortified plant-based products, individuals on vegan and vegetarian diets have several practical options for meeting their vitamin D needs. For consistent intake, including UV-treated mushrooms or fortified items in your diet is recommended. If dietary sources are insufficient, consulting a healthcare provider about supplements is advisable, especially for those with limited sun exposure. Healthline offers further reading on incorporating vitamin D into your diet.
