Vitamin D and Mushrooms

One of the most interesting things about mushrooms is their ability to increase the amount of vitamin D in their tissues when exposed to ultraviolet light. In that sense, they have something in common with us, although the biological mechanism is, of course, different.

Mushrooms growing outdoors naturally receive more sunlight, so they may contain more vitamin D. By contrast, many supermarket mushrooms are grown indoors, where they receive little or no ultraviolet light, so their vitamin D content is usually lower.

The interesting part is that this can still change after you bring them home. UV light acts on ergosterol naturally present in mushrooms and stimulates the formation of vitamin D2. That means sliced mushrooms can be left in sunlight for a while before cooking to increase their vitamin D content.

The more mushroom surface is exposed to UV light, the more effective this process can be, which is why sliced mushrooms may respond better than whole ones.

This does not mean that a few mushrooms left on the windowsill will solve a vitamin D deficiency, but it is a great example of how light can directly change the nutritional composition of mushrooms.