Most mushroom research stops at cells or animals. Vitamin D2 is an exception: researchers have followed a mushroom compound from the laboratory to a measured change in human blood. This article looks at how that was done, what the trials found, and where the limits are.
The chemistry in brief
Fungal cell membranes contain ergosterol, which plays the part cholesterol plays in animal cells. When ultraviolet light strikes ergosterol, it is converted to vitamin D2, also called ergocalciferol. It is the same kind of reaction that makes vitamin D3 in human skin in sunlight. Most cultivated mushrooms are grown in the dark and contain very little vitamin D2 unless they are exposed to sunlight or UV lamps after harvest. See Fungal Sterols Explained.
The key trial
Urbain et al., 2011 (Germany). Researchers treated fresh button mushrooms with UV-B light, which raised their vitamin D2 content from under 1 microgram to 491 micrograms per 100 g, and made them into a soup. Twenty-six young adults whose blood level of 25-hydroxyvitamin D, the standard measure of vitamin D status, was 50 nmol/L or below were randomly assigned to three groups. One group ate the UV-treated mushroom soup, one took a vitamin D2 supplement supplying the same amount, and one had a placebo. The dose was 28,000 IU once a week for four weeks, within a five-week study.
Blood levels rose in the mushroom group and were significantly higher than in the placebo group after two weeks. The rise was not different from that seen with the supplement. The researchers concluded that vitamin D2 from UV-treated mushrooms was absorbed and used as well as vitamin D2 from a supplement.
The trial was registered in advance, used a comparison supplement as well as a placebo, and measured a direct, objective outcome. It was also small, short and single-blinded, meaning the participants didn’t know which group they were in but the researchers did.
The pooled evidence
Cashman et al., 2016. A systematic review and meta-analysis gathered the randomised trials of UV-exposed mushrooms and described the results as limited and mixed. Its conclusion was that eating UV-exposed mushrooms may raise total vitamin D status when a person’s starting level is low. The detail matters: the D2 form in the blood went up, while the D3 form went down by a smaller amount, so the net gain was less than the rise in D2 alone would suggest.
D2 and D3 are not identical
Vitamin D3 is the form made in skin and found in animal foods. Vitamin D2 comes from fungi and yeast. Both raise blood levels of vitamin D, but a 2012 meta-analysis of trials comparing them found D3 more effective at raising and maintaining those levels. D2 from mushrooms is of particular interest to people who avoid animal products.
Reading the evidence together
- The outcome is a blood measurement. The trials show a change in vitamin D status. They were not designed to show effects on health.
- Starting level matters. The clearest effects were in people who began with low vitamin D.
- UV treatment is the whole point. Ordinary dark-grown mushrooms don’t provide meaningful vitamin D. Content depends on the UV dose, the species and how the mushrooms are stored and cooked.
- Food, not extract. Every trial used whole mushrooms or mushroom powder eaten as food.
What this doesn’t mean
These findings can’t be transferred to mushroom extracts. Our tinctures are made from mushrooms that have not been UV-treated, and are taken in millilitres, not portions. They are not a source of vitamin D and we don’t suggest otherwise. In the UK, government advice is that everyone should consider a daily supplement containing 10 micrograms of vitamin D during autumn and winter. The NHS website has current guidance, and your GP or pharmacist can advise on your own circumstances.
Why it’s a useful case study
The vitamin D2 story shows what a complete chain of evidence looks like. The compound is identified. The amount in the food is measured. People are randomly assigned to eat it or not. A specific, objective outcome is measured in their blood. A review then pools the trials and reports the mixed picture honestly. Most claims about functional mushrooms are missing several of those steps. See In Vitro, Animal and Human Studies.
What remains uncertain
- How much vitamin D2 UV-treated mushrooms on sale actually contain by the time they are eaten.
- How well mushroom vitamin D2 maintains vitamin D status over months and years.
- Whether the fall in the D3 form seen in trials matters.
Our approach
We describe our tinctures by what they are and how they’re made, not by what they might do, and we don’t present them as a source of any vitamin. For the wider picture, see Understanding Mushroom Science: A Beginner’s Guide.
References
- Urbain P, Singler F, Ihorst G, Biesalski HK, Bertz H. Bioavailability of vitamin D2 from UV-B-irradiated button mushrooms in healthy adults deficient in serum 25-hydroxyvitamin D: a randomized controlled trial. European Journal of Clinical Nutrition. 2011;65(8):965–971.
- Cashman KD, Kiely M, Seamans KM, Urbain P. Effect of ultraviolet light-exposed mushrooms on vitamin D status: liquid chromatography-tandem mass spectrometry reanalysis of biobanked sera from a randomized controlled trial and a systematic review plus meta-analysis. Journal of Nutrition. 2016;146(3):565–575.
- Tripkovic L, Lambert H, Hart K, et al. Comparison of vitamin D2 and vitamin D3 supplementation in raising serum 25-hydroxyvitamin D status: a systematic review and meta-analysis. American Journal of Clinical Nutrition. 2012;95(6):1357–1364.
Study titles are reproduced as published and are not claims made by Spore & Bloom.
