UV-Exposed Mushrooms
Food · Vegetable · Food, Typed Supps
More vitamin D than salmon, from a fungus that made it out of sunlight.
Stage by stage
- Ergosterol (The mushroom): The precursor is already there; ultraviolet light is what converts it.
- Photoconversion (UV light): The same reaction human skin performs, starting from a different molecule.
- Vitamin D₂ (Skeleton): 24.18 mcg per 100 g — more than salmon, and the highest non-animal source.
- D₂ vs D₃ (Liver): D₂ raises blood levels somewhat less efficiently than D₃, though it does work.
What the evidence supports
- Raising vitamin D status — moderate evidence. Photoconversion of fungal ergosterol yields ergocalciferol at 24.18 mcg/100 g, exceeding most oily fish. D₂ raises serum 25(OH)D less efficiently than D₃ microgram for microgram, but it is bioactive.
- Vitamin D from conventionally grown mushrooms — insufficient evidence. Mushrooms grown in darkness contain negligible vitamin D. The entire content depends on the UV step, so only labelled product qualifies.
Timing
Nothing to time. The one thing to get right is buying the labelled UV-exposed product rather than ordinary mushrooms.
Time to effect
- 6–12 weeks: How long blood vitamin D takes to respond to sustained intake.
- Hours: How long mushrooms need in sunlight to generate measurable vitamin D.
Allergens
None of the fourteen major allergens. Derived from what this food is, not from a product label.
Eating patterns
Fits: Vegan, Vegetarian, Pescatarian, Halal, Kosher, Keto, Gluten-free. Depends on the product: Low-FODMAP.
In season
September to November in the northern hemisphere, March to May in the southern.
Satiety
The satiety index is measured on 240 kcal servings. At 21 kcal per 100 g that is 1.1 kg of this, which is not a serving anyone eats — so the index has nothing to say about it.
Environmental footprint
0.5 kg CO2e and 108 litres of freshwater per kg, matched to "Other vegetables" in Poore & Nemecek (2018), Science 360.
Cost band
Cheap — roughly £2.5 per kg, as a band midpoint rather than a price.
Key nutrients
Nutrition per 100g
- Calories: 21
- Protein: 2.2g
- Carbohydrate: 1.3g
- Fat: 0.4g
- of which saturated: 0.1g
- Fibre: 1.4g
- Sodium: 9mg
Food vs. supplement
Vitamin D is the nutrient food supplies least well — sunlight does nearly all the work, and almost every dietary source is animal-derived. A fungus that manufactures it out of ultraviolet light is close to the only exception.
Kitchen tip
Leave them gills-up on a windowsill in direct sun for a couple of hours. The vitamin D goes up measurably, and it costs nothing.
Common myth
“Mushrooms are a good source of vitamin D.” In reality: Only if they have been exposed to ultraviolet light. Mushrooms grown in the dark — which is most of them — contain almost none. The UV-treated ones are labelled and carry 24.18 mcg per 100 g, more than salmon. You can also do it at home: a couple of hours gills-up in direct sunlight raises the vitamin D measurably.
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