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Shiitake benefits: 30 minutes of sunlight creates vitamin D

Ultraviolet light converts the ergosterol in shiitake into vitamin D2. Very few non-animal foods can do this.

Ingredient Health Benefits editorial team

Published Sep 3, 2026Updated Oct 12, 20262 min read

Not individually reviewed by a clinician.Editorial policy

Shiitake
Contents

What it is

Shiitake grows on the dead wood of oaks and related trees. It is native to East Asia and has been cultivated in Korea, China and Japan for centuries. It is one of the rare ingredients whose composition changes dramatically on drying: enzymes act during drying and rehydration and sharply increase guanylate, a savoury compound — which is why fresh and dried shiitake are used almost as two different ingredients. That flavour dissolves into the soaking water too, so the water is kept and used as stock. The stems are tough and are usually removed and used separately.

Scientific name Lentinula edodes

Mushrooms are fungi, not plants, and the place that difference shows up nutritionally is vitamin D. Shiitake contains the precursor ergosterol, which converts to vitamin D2 on exposure to ultraviolet light.

It is the same principle by which cholesterol in human skin becomes vitamin D3. Spreading dried shiitake in sunlight for thirty minutes to two hours multiplies its vitamin D content.

Key benefits

  1. Early research

    Beta-glucans modulate the immune response

    Shiitake's beta-glucans, lentinan among them, bind receptors on immune cells and modulate their response. Purified lentinan has been used in Japan as an adjunct therapy.[1]

  2. Nutrition data

    Sun-dried, it becomes a vitamin D source

    UV-exposed shiitake can reach tens of micrograms of vitamin D per 100 g. Mushrooms are effectively the only non-animal food carrying vitamin D, which matters a great deal in plant-based diets.

  3. Nutrition data

    Strong umami for the calories

    It is rich in guanylate, an umami compound, so dishes taste complete with less salt. That makes it a practical tool in a low-sodium diet.

  4. Early research

    There is research on cholesterol

    Animal studies suggest shiitake's eritadenine affects cholesterol metabolism. One randomised human trial exists (68 people, 66 days), and the only thing that moved was triglycerides, down 10% — total and LDL cholesterol did not budge. Despite the framing, there is still no human evidence for cholesterol itself.[2][3]

How to eat it well

  • Spread them in sunlight for at least 30 minutes before cooking. Dried or fresh, vitamin D rises. Gills facing up is more efficient.
  • Do not discard the soaking water from dried shiitake. The umami compounds are dissolved in it.
  • Cooking with oil improves absorption of vitamin D and other fat-soluble components.
  • Always cook fresh shiitake. Raw consumption is rarely linked to a distinctive dermatitis.
  • The stems are tough but perfectly usable chopped fine for stir-fries or stock.

How to read the grades

Each benefit carries a label showing how far research on people supports it. Grades differ between items even within the same ingredient.

Nutrition data
A fact verifiable from food composition databases or health authorities. This is a different kind of statement from a clinical effect.
Strong evidence
Consistently confirmed across randomised controlled trials or meta-analyses.
Moderate evidence
Human studies exist, but effect sizes are small or results are mixed.
Early research
Cell or animal work, or small preliminary studies.
Not established
Commonly claimed, but not confirmed in studies on people.

Claims that are not established

What to watch out for

  • Eating raw or undercooked shiitake occasionally causes shiitake dermatitis, a whip-like rash. Cooking it through prevents this.
  • Relatively high in purines, so consider the amount if you have gout.
  • Avoid with mushroom allergy.
  • On immunosuppressants, discuss high-dose mushroom extract supplements with your clinician. Culinary amounts are usually fine.
  • Because dried shiitake substitutes umami for salt, you generally need less seasoning alongside it.

Nutrition

Approximate values per 100 g edible portion.

Calories
34 kcal2%
Carbohydrates
6.8 g2%
Fiber
2.5 g9%
Protein
2.2 g4%
Selenium
5.7 µg10%
Copper
0.14 mg16%
Vitamin B3
3.9 mg24%
Potassium
304 mg6%

Percentages are of the US FDA Daily Value for adults and children 4 and over. National reference intakes differ by sex and age.

Calculate this alongside other ingredients →

Key nutrients

Dishes with this ingredient

Sources

The databases and health authorities this article's nutrition figures and health statements draw on.

  1. 1Consuming Lentinula edodes (Shiitake) Mushrooms Daily Improves Human Immunity: A Randomized Dietary Intervention in Healthy Young AdultsClinical trialDai X, et al. J Am Coll Nutr 2015PMID 25866155
  2. 2Lentinus edodes: a macrofungus with pharmacological activitiesResearch literatureBisen PS, et al. Curr Med Chem 2010PMID 20491636
  3. 3Effects of Shiitake Culinary-Medicinal Mushroom, Lentinus edodes (Agaricomycetes), Bars on Lipid and Antioxidant Profiles in Individuals with Borderline High Cholesterol: A Double-Blind Randomized Clinical TrialClinical trialSpim SRV, et al. Int J Med Mushrooms 2021PMID 34375514
  4. 4MFDS Food Composition Database · 식품안전나라Food composition database
  5. 5USDA FoodData CentralFood composition database
  6. 6NIH Office of Dietary SupplementsHealth authority
  7. 7PubMedResearch literature
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