Ergosterol is as ubiquitous in mushrooms as cholesterol is in humans. It is formed by an almost identical metabolic process, the mevalonate pathway. When mushrooms are exposed to ultraviolet light, ergosterol is converted to ergocalciferol, or vitamin D₂. Once ingested, vitamin D₂ is converted to calcidiol in the liver and eventually calcitriol, our active vitamin D₃, in the kidneys. There is clinical evidence demonstrating that ergocalciferol-D₂, although not as bioavailable as calcitriol, could improve vitamin D deficiency in humans (1,2,3).

Mushrooms are an excellent source of vitamin D₂, particularly if they have been exposed to ample UV light (4). Researchers found that when people consumed chanterelle mushrooms containing 14 mcg of ergocalciferol with their lunch, that their serum vitamin D levels improved as much as the group who was receiving ergocalciferol supplementation (5). However, another study found that vitamin D levels decreased significantly after cooking mushrooms and serum concentrations of vitamin D after consumption of 100 g fresh sliced cooked mushrooms for 16 weeks did not show significant improvement in serum vitamin D levels. This was, notably, in a prediabetic, overweight population (6). In healthy young adults, serum vitamin D levels did improve after consumption of vitamin D₂-enhanced button mushrooms via UV-B irradiation and to a similar degree as with a vitamin D₂ supplement (7).

The benefits of optimal serum vitamin D levels include and are not limited to:

Bone health, kidney health, immune modulation, calcium homeostasis, and cardiovascular health (8).

1. Vaes AMM, Tieland M, de Regt MF, Wittwer J, van Loon LJC, de Groot LCPGM. Dose-response effects of supplementation with calcifediol on serum 25-hydroxyvitamin D status and its metabolites: A randomized controlled trial in older adults. Clin Nutr. 2018;37(3):808-814. doi:10.1016/j.clnu.2017.03.029
2. Martineau AR, Thummel KE, Wang Z, et al. Differential Effects of Oral Boluses of Vitamin D2 vs Vitamin D3 on Vitamin D Metabolism: A Randomized Controlled Trial. J Clin Endocrinol Metab. 2019;104(12):5831-5839. doi:10.1210/jc.2019-00207
3. Seijo M, Mastaglia S, Brito G, Somoza J, Oliveri B. Es equivalente la suplementación diaria con vitamina D2 o vitamina D3 en adultos mayores? [Is daily supplementation with vitamin D2 equivalent to daily supplementation with vitamin D3 in the elderly?]. Medicina (B Aires). 2012;72(3):195-200.
4. Kamweru PK, Tindibale EL. Vitamin D and Vitamin D from Ultraviolet-Irradiated Mushrooms (Review). Int J Med Mushrooms. 2016;18(3):205-214. doi:10.1615/IntJMedMushrooms.v18.i3.30
5. Outila TA, Mattila PH, Piironen VI, Lamberg-Allardt CJ. Bioavailability of vitamin D from wild edible mushrooms (Cantharellus tubaeformis) as measured with a human bioassay. Am J Clin Nutr. 1999;69(1):95-98. doi:10.1093/ajcn/69.1.95
6. Mehrotra A, Calvo MS, Beelman RB, et al. Bioavailability of vitamin D2 from enriched mushrooms in prediabetic adults: a randomized controlled trial. Eur J Clin Nutr. 2014;68(10):1154-1160. doi:10.1038/ejcn.2014.157
7. 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. Eur J Clin Nutr. 2011;65(8):965-971. doi:10.1038/ejcn.2011.53
8. Charoenngam N, Holick MF. Immunologic Effects of Vitamin D on Human Health and Disease. Nutrients. 2020;12(7):2097. Published 2020 Jul 15. doi:10.3390/nu12072097