100g of regular store-bought mushrooms (ones that have not specifically been exposed to UV light/sunshine) provide approximately 20% of your daily vitamin D needs. However, some mushroom farmers are now exposing their mushrooms to a few seconds of UV light after harvesting to increase their vitamin D content. 100g of these specially labelled ‘vitamin D mushrooms’ provides 20µg of vitamin D, which is more than enough of the recommended daily intake of vitamin D.
You can create vitamin D mushrooms at home by leaving regular mushrooms in the sunlight! Studies show that a few hours of sun exposure will do the same thing (Simon et al 2011 and Phillips & Rasor 2013).
Phillips and Rasor (2013), ‘A nutritionally meaningful increase in the vitamin D in retail mushrooms is attainable by exposure to sunlight prior to consumption’, Nutrition & Food Sciences, 3(6).
Simon et al (2011), ‘Vitamin D mushrooms: comparison of the composition of button mushrooms (Agaricus bisporus) treated post-harvest with UVB light or sunlight’, Journal of Agricultural & Food Chemistry, 59(1): 8724-8732.