Does putting mushrooms in the sun give them vitamin D?
Yes: sliced mushrooms set out in midday sun for 15 to 30 minutes usually gain vitamin D2. In one small test, oyster and enoki gained the most. Here's the method, what's known about winter, and why it doesn't replace a supplement.
Derick5 min read
Yes: picked mushrooms make vitamin D2 in sunlight. Slice them or lay them gills up, give them 15 to 30 minutes around midday, then cook or refrigerate them. The catch: most numbers come from small tests on store-bought mushrooms, and results vary.
Our sources are published papers, checked 6 November 2026 (two as abstracts only). No number here comes from our own mushrooms. Cardwell, our main source, consulted for the Australian mushroom industry before September 2017.
Do mushrooms really make vitamin D in the sun?
Yes: UV-B in sunlight turns ergosterol in the mushroom into vitamin D2, and 15 to 120 minutes of midday sun usually takes button mushrooms from under 1 μg per 100 g to over 10 μg, which "approaches the daily requirement of vitamin D recommended in many countries" (Cardwell et al. 2018). That's over 280 IU per 70 g, about a cup (our conversion, at 40 IU per μg).
In Blacksburg, Virginia, vitamin D2 in sliced white button "rose 157-754 IU/70 g" in 15 minutes on clear middays (Phillips & Rasor 2013). Our PubMed search didn't find that paper, so treat its details as leads (our reading). A PubMed-listed study agrees on 15 minutes: sliced button reached 17.6 μg per 100 g in German midsummer (Urbain & Jakobsen 2015), about 490 IU/70 g (our conversion).
It can disappoint: a Danish study measured 0.9 μg per 100 g (about 25 IU per 70 g, our conversion) after about 20 minutes of midday sun and called that "surprising" (Kristensen et al. 2012).
How long should you leave mushrooms in the sun?
Leave them 15 to 30 minutes in direct sun around midday, sliced or gills up, in one layer.
- Slice them, or turn them gills up. Sliced mushrooms "produce more vitamin D2 than whole mushrooms" (Cardwell). Gills facing a controlled UV source did better in studies Phillips & Rasor cite; applying that to sun is our reading.
- Spread them outdoors, unshaded. One layer and no windowsill are our advice; we found no test through glass. Use foil or a pan: they showed "no measured difference", and white paper was "slightly lower" in one run (Phillips & Rasor).
- Aim for 9:30 am to 3:30 pm on a clear day. That paper's sliced button on foil gained, in IU per 70 g, 704 in 15 minutes and 1,142 in 30 on a clear 30 August; 181 in 15 and 512 in 60 on an overcast 12 October. Early or late under some cloud, 15 minutes gained far less: 7.3 (9:09 am, March) and 24 (5:07 pm, October).
- In full sun, stop at about 30 minutes. More than that "could be expected to affect the quality of the fresh mushrooms" (same paper). Under cloud, go longer if they still look fresh (our advice). The limit is quality, not D2 (our reading, timing included): sliced button being sun-dried gained for an hour, held to about four and showed "a significant decline" only at about six (Urbain & Jakobsen).
- Cook them, or refrigerate them. UV-exposed mushrooms "retain nutritionally relevant amounts of vitamin D2 when refrigerated for one week or less" (Cardwell; extending that to sun is our reading), but pink oysters last a day or two at best, shiitake 3 to 8 days.
Which mushrooms gain the most vitamin D in the sun?
In the one sun test we found comparing them, oyster and enoki gained the most: Phillips & Rasor, on foil in Blacksburg (37°N), 17 October 2011, store-bought mushrooms.
| Mushroom | Set out | Gain per 70 g in 15 min |
|---|---|---|
| Enoki | Whole | 886 IU |
| Oyster | Sliced | 832 IU |
| Shiitake | Sliced | 529 IU |
| Portabella | Sliced | 472 IU |
| White button | Whole | 154 IU |
| White button (four similar clear runs, same site) | Sliced | 233 to 704 IU |
Treat it as a lead: the authors call the data "preliminary". Their table puts enoki, shiitake and portabella at 1:30 pm and oyster and whole button at 3:30, with lower logged UV, so gaps across those slots aren't fair comparisons (our reading). They tie whole button's low score to fewer exposed gills; whole enoki did well anyway, though at 1:30.
Does it work in November or January?
Nobody we read tested November to January at northern US latitudes, so we can't promise it, and the farther north, the less likely (our reading). The closest evidence:
- Blacksburg (37°N), sliced button on foil: a clear 6 February at 12:52 pm gained 427 IU per 70 g in 15 minutes; a mostly cloudy 25 February at 9:51 am gained 78 (Phillips & Rasor).
- Winter in Sydney (July): an unpublished "personal communication" in Cardwell has whole button reaching 10 μg per 100 g in 1 to 2 hours, by size.
- Skin, not mushrooms: cloudless sun on skin samples in Boston (42.2°N) "from November through February produced no previtamin D3", yet it worked in midwinter at 34°N (Webb et al. 1988). UV-B works best in mushrooms too, so we'd expect a similar pattern (our reading).
Our advice: check your UV index. We found no cutoff for mushrooms, so take a low reading to mean longer, or wait: try from February around Virginia's latitude, March around Boston's, later farther north.
Can sunned mushrooms replace a vitamin D supplement?
No: eat them as food, and talk to a doctor about anything beyond that (our advice).
Mushrooms make D2, and "vitamin D3 is more effective than vitamin D2" at raising blood levels. Trials of UV-treated, not sunned, mushrooms are mixed: soup over five weeks, in adults starting low, worked "as effectively as supplemental vitamin D2"; meals over six weeks had "no effect" on vitamin D status overall (Cardwell). You can't measure your mushrooms' D2 at home (our reading).
Cooking costs some: button kept 88% pan-fried without oil for 5 minutes, 62-67% boiled for 20 or baked for 10 (Cardwell).
Should you put the growing block in the sun instead?
No: sun the picked mushrooms, not the block (our advice; we found no test of sunning one). Mushrooms can make D2 while growing, but in lamp-treated, compost-grown button, growth "diluted the vitamin D2 from 24 to 3 µg" per 100 g within 2 days (Kristensen); applying that to a block is our reading. Our guide keeps oyster blocks out of direct sun.
How do you note a sun test in Hypha?
Put it in the flush's notes: on a fruiting block's timeline in Hypha, tap Harvest Flush, or open the flush if you've already logged it, and add the time and sky under Notes. There's no vitamin D field, and Hypha can't measure it.
FAQ
Do sun-dried mushrooms have vitamin D?
They can, on thin evidence: sliced button being sun-dried reached about 3.9 μg per gram of dry weight in its first hour, then plateaued and later fell (Urbain & Jakobsen). Dried mushrooms sold in China averaged 16.9 μg per gram of dry matter, drying method unstated (Cardwell).