Vitamin D3, sourced from sunlight exposure, animal, and plant sources may be preferable to vitamin D2 sourced from fungi.
Years ago, it was shown that vitamin D isn't just the sunshine vitamin for us, but for mushrooms as well. You take some mushrooms, and 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 by at the store don't have any vitamin D because they're grown in the dark, but there are now there are sun-bathed varieties on the market that boast significant levels. Some mushrooms out grown in the wild have some as well, but only about 12% of one's recommended daily allowance per cup. But is the vitamin D bioavailable? 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, but after doing his own research this patient decided to self-treat. He bought a UV bulb from a local hardware shop and proceeded to shine this directly onto 2 cups of regular mushrooms a day, before stir-frying and consuming them. He repeated this on a daily basis for 3 months, and indeed his vitamin D levels 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 just 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 serum 25-hydroxyvitamin 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 the placebo mushroom soup. The type of D made by mushrooms is vitamin D2, which is typically derived from yeast and is the form traditionally prescribed by doctors to cure D deficiency (drisdol). 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 as effective as D3 in maintaining one's vitamin D levels at standard daily dosing levels. Whether folks were given D3, D2, or a combo of half D3 and D2 it didn't seem to matter much in terms of improving vitamin D levels in the bloodstream. But that was 5 years ago—what's the update? Is vitamin D2 better than vitamin d3? It depends how you take it and what your starting levels are. Taken daily in doses up to 4000 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 megadoses on a weekly or monthly basis in doses up to 50,000 units at a time, D3 works better than D2. And if you're not vitamin D deficient, if vitamin D levels are normal, for example, if you live in California and get enough sun, then taking D2 from 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, though, is because of the benefits we expect to get from those levels, such as a longer lifespan. The latest Cochrane review on vitamin D and mortality found that while D3 supplementation was able to reduce mortality other forms of vitamin D, including D2, did not. This may be because most of the D2 trials used megadosing regimens up to 300,000 units injected into people, but 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 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 (sheep) and non-animal (Cladina arbuscula) sources of vitamin D3 supplements.
To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring watch the above video. This is just an approximation of the audio contributed by Jonathan Hodgson.
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How much D should those who can't get enough sun take? I now recommend 2000 iu a day. That's not what the Institute of Medicine says though. I justify my recommendation on a two-week video series that starts with Vitamin D Recommendations Changed and ends with Resolving the Vitamin D-Bate. What about tanning beds? See Vitamin D Pills vs. Tanning Beds. I also recommend to Take Vitamin D Supplements With Meals. What's that bit about vitamin D and longevity? See Vitamin D and Mortality May Be a U-shaped Curve. You know I'm averse to mentioning brand names, but please feel free to leave any recommendations in the comments for cheap sources.
I still think people should eat mushrooms though! For starters, see:
Check out my blog post for additional context: Vitamin D from Mushrooms, Sun, or Supplements?
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