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Mushrooms and vitamin D2: what UV changes

By Claire Mercier · Nutritionist, MSc5 min readPublished 09/14/2026
Sources
4
Validated claims
3
Dominant evidence
Limited
Freshness
09/14/2026
Mushrooms and vitamin D2: what UV changes

Cultivated mushrooms are not automatically rich in vitamin D. Their interest comes from a precise mechanism: ergosterol, a mushroom compound, can be converted into vitamin D2 (ergocalciferol) by UV light. The difference between an ordinary mushroom and a UV-treated mushroom is therefore decisive.

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1. What happens to ergosterol under UV light? Mushrooms contain ergosterol in their membranes. UV light, especially UV-B, first converts it to pre-vitamin D2; heat then favors conversion to vitamin D2. This resembles skin vitamin D synthesis, but the final product is mainly D2 rather than D3.

The result is not identical every time. Species, exposed surface, intensity, season, latitude, weather and duration all matter. Slicing increases exposed surface, but cannot predict the final home-produced amount precisely.

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2. Which varieties should you choose? Research focuses mainly on button mushrooms (*Agaricus bisporus*), shiitake (*Lentinula edodes*) and oyster mushrooms (*Pleurotus*). Some wild chanterelles can contain more D2, but levels vary widely. Ordinary white, brown, portobello, shiitake or oyster mushrooms are not necessarily enriched: the label and producer analysis are more reliable than color or name.

Look for “UV-treated”, “UV-exposed” or a vitamin D amount in micrograms. Standard retail mushrooms should not be presented as a major source without measurement; several composition databases find less than 1 µg D2 per 100 g in non-exposed retail products.

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3. Can you put them in sunlight at home? Studies use controlled conditions. Sliced mushrooms exposed to midday sunlight for 15 to 120 minutes sometimes exceeded 10 µg D2 per 100 g, but location, season and surface strongly affect results. This is not a way to measure or treat deficiency.

If you try it as a kitchen experiment, use only clean, intact edible store-bought mushrooms, place them in one layer, refrigerate them afterwards and eat them promptly. Never look directly at a UV lamp or use a household UV lamp: UV can damage skin and eyes. Sunlight must never replace sun protection.

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4. Storage and cooking: how much remains? UV-treated mushroom D2 generally lasts several refrigerated days, but no universal duration applies to every species and condition. A review suggests about one week as a reasonable guide; newer work reports around 7 to 10 days of stability for refrigerated *A. bisporus*.

Cooking does not remove all D2. Studies report method-dependent retention, about 62–67% after boiling or oven cooking in one protocol and up to 88% after pan-cooking without oil. These are experimental results, not a guarantee for every recipe. Human bioavailability after cooking is still uncertain.

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5. D2 or D3: are they equivalent? Mushroom D2 is usable by the body, and human studies show higher blood markers after eating UV-treated mushrooms. Comparative evidence often finds that D3 raises blood levels more or for longer. D2 can still complement the diet, especially for plant-based eaters, but it cannot promise to correct an individual deficiency.

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Bottom line Prefer a product that states its vitamin D content or UV treatment. Ordinary mushrooms remain useful foods, but their D2 content should not be assumed. UV, slicing, refrigeration and cooking change the result; variability is the key limitation. If a deficiency has been diagnosed, ask a health professional which strategy and monitoring are appropriate.

Sources

Peer-reviewed studies and institutional references used for this article.

  1. 1NIH Office of Dietary Supplements· 2025
    Established
    View source
  2. 2Cleveland Clinic· 2025
    Limited
    View source
  3. 3Frontiers in Nutrition· 2024
    Limited
    View source
  4. 4Phillips et al.· 2018
    Literature reviewLikely
    View source

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By

Claire Mercier

Registered nutritionist focused on whole-food diets and metabolic health.

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