Photobiology of vitamin D in mushrooms and its bioavailability in humans

Mushrooms exposed to sunlight or UV radiation are an excellent source of dietary vitamin D(2) because they contain high concentrations of the vitamin D precursor, provitamin D(2). When mushrooms are exposed to UV radiation, provitamin D(2) is converted to previtamin D(2). Once formed, previtamin D(2) rapidly isomerizes to vitamin D(2) in a similar manner that previtamin D(3) isomerizes to vitamin D(3) in human skin. Continued exposure of mushrooms to UV radiation results in the production of lumisterol(2) and tachysterol(2). It was observed that the concentration of lumisterol(2) remained constant in white button mushrooms for up to 24 h after being produced. However, in the same mushroom tachysterol(2) concentrations rapidly declined and were undetectable after 24 h. Shiitake mushrooms not only produce vitamin D(2) but also produce vitamin D(3) and vitamin D(4). A study of the bioavailability of vitamin D(2) in mushrooms compared with the bioavailability of vitamin D(2) or vitamin D(3) in a supplement revealed that ingestion of 2000 IUs of vitamin D(2) in mushrooms is as effective as ingesting 2000 IUs of vitamin D(2) or vitamin D(3) in a supplement in raising and maintaining blood levels of 25-hydroxyvitamin D which is a marker for a person's vitamin D status. Therefore, mushrooms are a rich source of vitamin D(2) that when consumed can increase and maintain blood levels of 25-hydroxyvitamin D in a healthy range. Ingestion of mushrooms may also provide the consumer with a source of vitamin D(3) and vitamin D(4).