Mushrooms: the vitamin D depends on the light

Two claims follow mushrooms around, and they do not carry the same weight. The vitamin D is real and it comes from light. A pooled analysis of irradiation experiments found an optimum for sliced white mushrooms at which they reached 16.27 micrograms of vitamin D2 per gram (95% CI 13.69 to 18.85), with the vitamin degrading again above that point. That is the modelled optimum of a laboratory irradiation experiment rather than the punnet in your shop, and the paper gives the number per gram without saying whether the gram is fresh or dried, so you cannot turn it into a portion. NIH says the native amount varies from mushroom to mushroom, and that the FDA has approved UV-treated mushroom powder as an added source of D2, which tells you the light was doing the work. The cancer and mortality numbers read stronger than they are. Pooling 17 observational studies gave 34 percent lower total cancer risk in the highest intake group (RR 0.66, 95% CI 0.55 to 0.78), and 11 of those 17 were case-control studies, where people are asked what they used to eat after they are already ill. One paper shows the problem inside itself. Its own cohort of 30378 US adults had 30 percent lower mortality among mushroom eaters (HR 0.70, 95% CI 0.56 to 0.88) until diet quality and lifestyle entered the model, after which the association was gone (HR 0.84, 95% CI 0.67 to 1.06). Watch what was actually fed, too. Several of the trials on this page used an encapsulated extract, a freeze-dried powder dosed by body weight, or bread baked with maitake. None of those is a pan of mushrooms. One warning about the sections below. The heading about safety, limits and interactions holds two cards, and both of them are effectiveness trials, one of a maitake bread and one of an extract capsule. We hold no card on an upper limit, on a drug mushrooms interact with, or on who should be careful with them.

The numbers, per 100 g

How much is actually in it

• A weighted meta-analysis modelled a UV-B optimum for sliced Agaricus bisporus at 16664 J/m2 and 3.2 W/m2, at which laboratory irradiation yielded 16.27 micrograms of vitamin D2 per gram (95% CI 13.69 to 18.85). The abstract does not say whether that gram is fresh or dried mushroom, so the number cannot be turned into a portion. — pooled UV irradiation experiments on edible mushrooms, modelled by response surface methodology Evidence A source
  16.27 micrograms vitamin D2 per gram (95% CI 13.69 to 18.85) at the modelled optimum of a laboratory irradiation experiment, with degradation above it. The mass basis, fresh or dried, is not stated in the abstract
• NIH states that mushrooms carry variable amounts of vitamin D2 and that FDA has approved UV-treated mushroom powder as a food additive source of vitamin D2. — US food supply, NIH Office of Dietary Supplements fact sheet for health professionals Evidence E source
  Variable native vitamin D2 content, raised deliberately by UV treatment

What your body absorbs

• The GLP-1 response to a meal fortified with oyster mushroom powder appeared only in the 16 participants whose gut microbiota had lower evenness (p = 0.012). — 16 adults with impaired glucose tolerance, median age 33.5 years, mean BMI 34.4, randomised crossover meal study (n = 16) Evidence B source
  Greater GLP-1 response after the enriched meal only in participants with lower microbial evenness (p = 0.012), NEFA response unaffected

What it does to your health

• Across 11 pooled case-control studies with 3900 gastric cancer cases, the highest mushroom consumption category carried 18% lower risk than the lowest (RR 0.82, 95% CI 0.71 to 0.95). — 3900 gastric cancer cases and 7792 controls from 11 studies in the Stomach Cancer Pooling Project (n = 11692) Evidence C source
  RR 0.82 (95% CI 0.71 to 0.95) highest against lowest, 0.77 (95% CI 0.63 to 0.95) across all 15 studies
• Pooling 17 observational studies, the highest mushroom intake group had 34% lower total cancer risk than the lowest (RR 0.66, 95% CI 0.55 to 0.78). — 17 observational studies published 1966 to October 2020, 11 of them case-control (n = 17 studies) Evidence C source
  Total cancer RR 0.66 (95% CI 0.55 to 0.78), breast cancer RR 0.65 (95% CI 0.52 to 0.81)
• Across five prospective cohorts covering 601893 people, mushroom eaters had 6% lower all-cause mortality (pooled risk ratio 0.94, 95% CI 0.91 to 0.98). — 601893 adults in five prospective cohort studies (n = 601893) Evidence C source
  Pooled risk ratio 0.94 (95% CI 0.91 to 0.98) for all-cause mortality
• Before adjustment the same cohort showed a 30% lower mortality risk for mushroom eaters (HR 0.70, 95% CI 0.56 to 0.88), and the association disappeared when lifestyle and diet quality entered the model. — 30378 adults in NHANES 2003 to 2014, age and sex adjusted model (n = 30378) Evidence C source
  HR 0.70 (95% CI 0.56 to 0.88) age and sex adjusted, against HR 0.84 (95% CI 0.67 to 1.06) fully adjusted
• Adding 84 g/d of white button and oyster mushrooms to a Mediterranean pattern for 8 weeks improved fasting serum glucose in 60 adults and changed no other cardiometabolic risk factor. — 60 adults aged 46, BMI 28.3, all food provided, 84 g/d of Agaricus bisporus 4 days a week and Pleurotus ostreatus 3 days a week for 8 weeks (n = 60) Evidence B source
  Fasting glucose change -2.9 mg/dL against +0.6 mg/dL in control, time by group P = 0.034, no change in blood pressure, lipids or insulin
• Freeze-dried oyster mushroom powder at 50 mg per kg body weight lowered fasting and postprandial serum glucose in healthy volunteers and postprandial glucose in people with type 2 diabetes (P < 0.05). — healthy volunteers and diet-controlled type 2 diabetes patients, single dose of 50 mg/kg body weight followed by a glucose load Evidence B source
  Significant reduction in fasting and postprandial serum glucose (P < 0.05), raised serum insulin in the diabetes group

Safety, limits and interactions

• In a trial of bread with maitake given daily for 11 to 18 weeks, the overall incidence of upper respiratory infection episodes did not differ from placebo. — healthy adults aged 18 to 20 and 40 to 85, bread with one of two maitake strains or placebo, 11 weeks in the young group and 18 weeks in the older group Evidence B source
  No difference in URTI incidence, fewer cumulative days of fever and runny nose with one strain only. This is an effectiveness trial. It says whether the bread worked, not how much is safe, what it interacts with or who should avoid it
• A mushroom extract blend taken for 12 weeks by 50 stressed adults lowered anxiety scores against placebo at 6 weeks (HAM-A p = 0.002) and at 12 weeks (p = 0.002). — 50 adults aged 22 to 55 in Malaysia with at least three stress-related symptoms, randomised to an encapsulated mushroom extract or placebo for 12 weeks (n = 50) Evidence B source
  HAM-A p = 0.002 at both 6 and 12 weeks, BDI p < 0.001 at 6 weeks, PSQI p < 0.001 at 12 weeks. This is an effectiveness trial of a capsule. It says whether the extract worked, not how much is safe, what it interacts with or who should avoid it

What people believe that the data does not support

• The EU register holds 4 mushroom health claims and has authorised none of them, including the oyster mushroom claim about natural immunological defences. — EU Register on nutrition and health claims, snapshot 2026-09-21, 2330 claims (n = 4 claims) Evidence E source
  0 authorised, 4 non-authorised under the name mushroom

Who this works differently for

• In 341519 adults followed for a median 13.4 years, a pooled intake of apple or pear, banana, mushrooms and onion or garlic did not reach significance for Crohn's disease risk (aHR 0.58, 95% CI 0.33 to 1.02, an interval that crosses 1). Only the trend across quartiles was significant (P trend 0.03), and mushrooms were not separated from the other three foods. — 341519 adults in the European Prospective Investigation into Cancer and Nutrition, 149 Crohn's cases and 379 ulcerative colitis cases (n = 341519) Evidence C source
  AHR 0.58 (95% CI 0.33 to 1.02) fourth against first quartile for Crohn's disease, so the interval crosses 1 and the association is not significant. Significant only as a trend across quartiles (P trend 0.03), for a four-food pooled exposure

What is still unknown

• The same paper's own cohort of 30378 US adults found no significant mortality association once diet quality was accounted for (HR 0.84, 95% CI 0.67 to 1.06). — 30378 adults in NHANES 2003 to 2014, mean follow-up 6.7 years, 2855 deaths (n = 30378) Evidence C source
  HR 0.84 (95% CI 0.67 to 1.06), not significant after full adjustment

The bottom line

When mushrooms were fed as food, one thing moved. Sixty adults added 84 g a day of white button and oyster mushrooms to a Mediterranean pattern for 8 weeks, and every meal was provided. Fasting glucose fell 2.9 mg/dL against a rise of 0.6 mg/dL in the control group (time by group P = 0.034). Blood pressure, blood lipids and insulin did not change. A single dose of freeze-dried oyster mushroom powder at 50 mg per kg of body weight lowered fasting and post-meal glucose in healthy volunteers and post-meal glucose in people with diet-controlled type 2 diabetes (P < 0.05). That is a powder weighed out on a scale. Nobody served anyone a meal. In a crossover meal study of 16 adults with impaired glucose tolerance and a mean BMI of 34.4, the extra GLP-1 response to a meal enriched with oyster mushroom powder showed up only in those whose gut bacteria were less evenly spread (p = 0.012). Sixteen people is a hint about who might respond, and nothing more, and their blood sugar was already out of range before the meal. The immunity story does worse under testing. Bread baked with maitake, eaten daily for 11 to 18 weeks, left the number of upper respiratory infections no different from placebo. The EU register holds four health claims filed under the name mushroom and has authorised none of them, including the oyster mushroom claim about natural immunological defences. On mood there is one trial: 50 stressed adults in Malaysia took an encapsulated mushroom extract for 12 weeks and scored lower for anxiety than placebo at 6 weeks and at 12 weeks (HAM-A p = 0.002 both times). One trial, 50 people, capsules. The gut finding people quote is thinner still. In 341519 adults followed for a median of 13.4 years, a pooled intake of apple or pear, banana, mushrooms and onion or garlic came out at an adjusted hazard ratio of 0.58 for Crohn's disease (95% CI 0.33 to 1.02). That interval crosses 1, so the association did not reach significance. What was significant is the trend across quartiles (P trend 0.03), and mushrooms were never separated from the other three foods. Now the gap, because it is the part you would want most. We hold no card that gives an upper limit for mushrooms, names a drug they interact with, or says who should be careful with them. The two cards filed under safety are effectiveness trials of a maitake bread and an extract capsule, so they answer a different question. Silence in our evidence base is not the same as a clean safety record, and you should read this page knowing that line is blank. If you take medication for blood sugar, the glucose findings above are a reason to talk to whoever prescribes it before you start eating mushrooms by the plateful. Our own USDA table carries 28 mushroom entries, white button, crimini, portabella, shiitake, oyster, maitake, enoki and more, and one of them is white mushroom exposed to ultraviolet light. They are listed separately because they are not the same food.

Sources

1. mush-r4-07 · meta-analysis of irradiation experiments
   For sliced Agaricus bisporus, an optimum was identified at 16,664 J/m2 and 3.2 W/m2, yielding 16.27 μg/g vitamin D₂ (95% CI: 13.69-18.85).
   Food Res Int, 2026 · checked 2026-09-23
2. mush-r4-08 · agency fact sheet
   Mushrooms provide variable amounts of vitamin D2 [17]. Some mushrooms available on the market have been treated with UV light to increase their levels of vitamin D2. In addition, the Food and Drug Administration (FDA) has approved UV-treated mushroom powder as a food additive for use as a source of vitamin D2 in food products [18].
   NIH Office of Dietary Supplements, Vitamin D fact sheet for health professionals · checked 2026-09-23
3. mush-r4-12 · randomised crossover, secondary analysis
   Notably, only participants with lower microbial evenness showed a greater GLP-1 response after EN versus CON (p = 0.012).
   Mol Nutr Food Res, 2025 · checked 2026-09-23
4. mush-r4-01 · pooled case-control analysis
   Higher mushroom consumption was associated with a lower risk of gastric cancer [relative risk (RR) for the highest vs. lowest consumption categories, 0.82; 95% confidence interval (CI), 0.71-0.95].
   Eur J Cancer Prev, 2023 · checked 2026-09-23
5. mush-r4-02 · meta-analysis of observational studies
   Higher mushroom consumption was associated with lower risk of total cancer (pooled RR for the highest compared with the lowest consumption groups: 0.66; 95% CI: 0.55, 0.78; n = 17).
   Adv Nutr, 2021 · checked 2026-09-23
6. mush-r4-03 · meta-analysis of prospective cohorts
   The meta-analysis of prospective cohort studies, including 601,893 individuals, showed that mushroom consumption was associated with a lower risk of all-cause mortality (pooled risk ratio: 0.94; 95% CI: 0.91, 0.98).
   Nutr J, 2021 · checked 2026-09-23
7. mush-r4-05 · prospective cohort
   In the age- and sex-adjusted model (model 1), individuals with mushroom consumption had a lower risk of all-cause mortality compared with those without mushroom consumption (adjusted hazard ratio (HR) = 0.70; 95% CI: 0.56-0.88; Table 2).
   Nutr J, 2021 · checked 2026-09-23
8. mush-r4-06 · randomised controlled feeding trial
   Consuming a Mediterranean-style healthy dietary pattern with 1 serving/d of whole Agaricus bisporus and Pleurotus ostreatus mushrooms improved fasting serum glucose but did not influence other established or emerging CMD risk factors among middle-aged and older adults classified as overweight or obese but with clinically normal cardiometabolic health.
   J Nutr, 2024 · checked 2026-09-23
9. mush-r4-13 · randomised controlled trial
   The P.o and P.c showed a significant reduction (P < 0.05) in fasting and postprandial serum glucose levels of healthy volunteers and reduced the postprandial serum glucose levels and increased the serum insulin levels (P < 0.05) of Type 2 diabetic patients.
   Phytother Res, 2015 · checked 2026-09-23
10. mush-r4-10 · randomised double-blind placebo-controlled trial
    While the overall incidence of URTI episodes did not differ between groups, symptom-specific analyses suggested strain-dependent differences.
    Food Funct, 2026 · checked 2026-09-23
11. mush-r4-11 · randomised double-blind placebo-controlled trial
    Anxiety, assessed by STAI-S and HAM-A, showed greater reductions in the Restake group at both 6 weeks (STAI-S: p = 0.025; HAM-A: p = 0.002) and 12 weeks (STAI-S: p = 0.011; HAM-A: p = 0.002).
    Brain Behav, 2026 · checked 2026-09-23
12. mush-r4-09 · regulatory register entry
    POL-HC-7765 Pleurotus ostreatus (oyster mushroom) Contributes to natural immunological defences Non-authorised
    EU Register on nutrition and health claims, claim POL-HC-7765, snapshot 2026-09-21 · checked 2026-09-23
13. mush-r4-14 · prospective cohort
    Pooled consumption of apple/pear, banana, mushrooms, and onion/garlic was associated with a lower risk of CD (fourth vs first quartile aHR 0.58; 95% CI: 0.33-1.02, P trend 0.03).
    Am J Gastroenterol, 2026 · checked 2026-09-23
14. mush-r4-04 · prospective cohort
    In our analysis of continuous NHANES, we found a non-significant association between mushroom consumption and all-cause mortality (adjusted hazard ratio (HR) = 0.84; 95% CI: 0.67-1.06) after adjusting for demographic, major lifestyle factors, overall diet quality, and other dietary factors, including total energy.
    Nutr J, 2021 · checked 2026-09-23