Vitamin D and tanning mushrooms

You have probably heard that vitamin D is obtained from being in the sun. But did you know that vitamin D is also produced in mushrooms when they are exposed to the sun during growth, harvesting, and cutting?

Vitamin D is an essential substance for our bodies, even though it is not a true vitamin. Vitamins are the substances that our body needs but cannot form on its own. Vitamin D, however, can be produced in our bodies when our skin is exposed to the ultraviolet light of the sun. We usually do not produce enough of it and thus need to obtain it through food. So it is considered a vitamin even though it does not exactly fit the definition.

Vitamin D aids in the absorption of calcium, magnesium, and phosphates from our gut, as well as helping to incorporate these minerals into our bones and teeth, and also contributes to the normal functioning of our immune system and cellular division.
Where do we get vitamin D?

Various recommendations suggest that an adult needs 10-20 µg of vitamin D each day. Of this, 5 µg should be consumed and the rest should come from our skin. But people are very different and we all live in very different parts of the world and climates. For example, in India, where there is enough sun throughout the year, people get their dose of sun quite easily. In the warmer parts of the year for those of us in temperate climates, we get enough vitamin D by exposing our hands and face to moderate sunlight for 15 minutes. Since we often do not get enough vitamin D during winter, it must be consumed in our food.

Large amounts of vitamin D are only rarely found in foods, with vegetable foods almost entirely lacking. That being said, animal-based foods also generally lack it, with only some fish, eggs, and liver having a large amount. You would need to eat a crazy 15 eggs per day to meet your needs! Many products, however, are fortified with vitamin D and thus contain a fair amount of it, for example vegetable milks, breakfast cereals, and vitamin drinks. Mushrooms, as we are about to see, can also be a good source of vitamin D.

Mushrooms contain a slightly different form of vitamin D that that produced in our skin and found in animal products; animals contain D3 while mushrooms contain D2. D2 is also the vitamin added to nutritional supplements and enriched foods because it is easier to produce, being harvested from yeast. Some research suggests that D2 may be less effective in our bodies, but the findings are not conclusive. Any difference that may exist, however, is not large. The European Food Safety Authority (EFSA) regards both forms as equivalent.
How much vitamin D do mushrooms have?

Naturally harvested mushrooms contain up to 60 µg of vitamin D per serving of 100 g of mushrooms. That is enough vitamin D for 4 days without sun or for 12 days with an average sun exposure in Europe. On the other hand, cultivated mushrooms, which mostly grow in the dark, contain very little vitamin D, usually below 1 µg per 100 g serving. Some manufacturers expose their mushrooms to ultraviolet light before picking to promote vitamin D production, but this is rare.
Can you sunbathe bought mushrooms to get more vitamin D?

One study on vitamin D in mushrooms exposed whole mushrooms to the sun for 2.5 hours on a clear day in California. The analysis showed that before sunbathing, the mushrooms contained only 0.5 µg of vitamin D and after sunbathing as much as 25 µg in a 100 g portion.

In another study, similar mushroom sunbathing was carried out in Germany, not far from the Swiss border. Mushrooms that had been harvested the previous day were sliced into 9 mm thick slices and sunbathed in the middle of a clear summer day. After 15 minutes of sunbathing, the vitamin D content of the mushrooms increased from a negligible 0.2 µg / 100 g to a considerable 17 µg / 100 g of fresh weight. Vitamin D production slowed down slightly after sunbathing, so that it took 45 minutes for the content to double to 32 µg / 100 g, and after sunbathing, vitamin D completely stopped. However, if after 1 hour the slices were turned so that the other side was exposed to the sun, they reached 60 µg / 100 g in the subsequent hour of tanning. That’s about as much vitamin D as mushrooms from nature contain. Similar research with similar results has been repeated with various other cultivated mushrooms, such as shitakes. The content 60 µg of vitamin D in a portion of 100 g of mushrooms is 60 x more than an eggs, which contains cca 1 µg of vitamin D per egg weighting 60 g; it is also 40 x more than a 100 g portion of beef liver, and 4 x more than a 100 g portion of fish.

Research has also been conducted where volunteers with vitamin D deficiency consumed sun-dried mushrooms for several weeks and then measured their vitamin D blood levels. These mushrooms were just as good a source of vitamin D as the equivalent amounts of other foods or nutritional supplements.

So, are you worried about lying out in the sun to get your vitamin D? Fear no more, our fungal friends have got our backs!

Additional reading:

Cardwell G, Bornman JF, James AP, Black LJ. A Review of Mushrooms as a Potential Source of Dietary Vitamin D. Nutrients. 2018;10(10):1498. Published 2018 Oct 13. doi:10.3390/nu10101498

Mau J.L., Chen P.R., Yang J.H. Ultraviolet irradiation increased vitamin D2 content in edible mushrooms. J. Agric. Food Chem. 1998;46:5269–5272. doi: 10.1021/jf980602q.

Nölle N., Argyropoulos D., Ambacher S., Muller J., Biesalski H.K. Vitamin D2 enrichment in mushrooms by natural or artificial UV-light during drying. Food Sci. Technol. 2016;85:400–404.

Simon R.R., Phillips K.M., Horst R.L., Munro I.C. Vitamin D mushrooms: Comparison of the composition of button mushrooms (Agaricus bisporus) treated post-harvest with UVB light or sunlight. J. Agric. Food Chem. 2011;59:8724–8732. doi: 10.1021/jf201255b.

Simon, R. R., Borzelleca, J. F., DeLuca, H. F., & Weaver, C. M. (2013). Safety assessment of the post-harvest treatment of button mushrooms (Agaricus bisporus) using ultraviolet light. Food and Chemical Toxicology, 56, 278–289. doi:10.1016/j.fct.2013.02.009

Mau, J.-L., Chen, P.-R., & Yang, J.-H. (1998). Ultraviolet Irradiation Increased Vitamin D2Content in Edible Mushrooms. Journal of Agricultural and Food Chemistry, 46(12), 5269–5272. doi:10.1021/jf980602q

Urbain, P., & Jakobsen, J. (2015). Dose–Response Effect of Sunlight on Vitamin D2 Production in Agaricus bisporus Mushrooms. Journal of Agricultural and Food Chemistry, 63(37), 8156–8161. doi:10.1021/acs.jafc.5b02945

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