 Years ago, it was shown that vitamin D isn't just the sunshine vitamin for us, but for mushrooms as well. You take some shiitakes, for example, put them under a sun lamp for an hour, and they make vitamin D just like we do, lounging at the pool. Now most mushrooms you buy at the store don't have any vitamin D, because they're grown in the dark. But there are now sun bathed varieties on the market that boost significant levels, even now available in sprinkled form. Some mushrooms grown outside in the wild may have some as well, but only about 12% of ones recommended daily allowance per cup. Is the vitamin D in mushrooms bioavailable, though? In 2008 there was a case report of a dark-skinned individual living in England in the winter, who, like the other 9 out of 10 South Asians living in the UK, was vitamin D deficient. His physician prescribed a vitamin D supplement, however, after doing his own research the patient decided to self-treat. He bought a UV bulb from a local hardware store, and proceeded to shine this directly onto two cups of regular mushrooms a day, before stir-frying and consuming them. He repeated this on a daily basis for three months, and indeed his vitamin D level shot up and he was cured. So it's reasonable to assume that such mushrooms may be able to provide a source of vitamin D for those at risk for deficiency. This was only one person, though, so further studies are necessary, and finally those studies have been done. Bioavailability of vitamin D from ultraviolet light-irradiated button mushrooms in healthy adults deficient in vitamin D, a randomized controlled trial. They compared the mushrooms to vitamin D supplements to placebo, and both the mushrooms and the supplements were equally effective in raising D levels compared to placebo. The type of vitamin D made by mushrooms, though, is vitamin D2, which is typically derived from yeast, and is the form traditionally prescribed by doctors to cure vitamin D deficiency. Most supplements, though, are D3, which is the type found in plants and animals, and typically derived from sheep's wool. Back in 2008 it was established that vitamin D2 was effective as D3 in maintaining one's vitamin D levels at standard daily doses, where their folks were given D2, D3, or a combination of half D2, half D3, and it didn't seem to matter much in terms of improving vitamin D levels in their bloodstreams. But that was five years ago. What's the update? Is vitamin D2 better than vitamin D3? It apparently depends on how much you take and what your starting levels are. Taken daily and doses up to 4,000 units a day, there appears to be no significant difference in the ability of D2 or D3 to raise vitamin D levels. But if you take mega-doses on a weekly or monthly basis and doses up to 50,000 units at a time, D3 works better than D2. And if you're not vitamin D deficient, if your vitamin D levels are normal, for example, you live in California and get enough sun, then D2 for mushrooms or supplements doesn't appear to raise your levels further. But if your levels are fine, why take supplements in the first place? The only reason we care about the levels in our blood is because of the benefits we expect to get from those levels, such as a longer life span. The latest Cochrane review on vitamin D immortality found that while D3 supplementation may be able to reduce mortality, other forms of D, including D2, did not. This may be because most of the D2 trials used mega-dosing regimens up to 300,000 units injected into people. But you know, until we have good data suggesting D2 supplementation can actually extend one's life, D3, the type of vitamin D found in animals and plants, may be preferable to vitamin D2, the vitamin derived from fungi. The best animal to get D3 from is yourself. But if you live at a latitude where you're not able to make enough, then there are both animal and non-animal sources of vitamin D3 supplements.