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Why Mushrooms are a Poor Source of Vitamin D
There are some articles and infographics going around that make a claim that mushrooms are a good source of Vitamin D, when in fact mushrooms are a poor source of vitamin D. For instance, this article on the Top 10 Foods Highest in Vitamin D shows mushrooms to be a ‘good source of vitamin d’. While the name of the article is correct, these ARE the top ten foods highest in Vitamin D, that is only because almost no foods have any significant amount of vitamin D, and there are no Vitamin D Vegetables or Vitamin D fruits at all. So in order to even get 10 foods, the author had to include foods with barely detectable levels of vitamin d- as is the case with mushrooms.
The article is misleading and at times patently incorrect because most of these foods cannot provide any meaningful amount of vitamin D that is necessary to provide even the minimum daily requirements, let alone the amount needed for disease prevention. As I point out in my article on Vitamin D Foods, to meet your vitamin D needs you’d have to eat such incredibly high quantities that it would be impossible, impractical, or exorbitantly expensive to do.
Where This Bad Information is Coming From
This information is coming from some studies on the vitamin d, including this one entitled Vitamin D and Sterol Composition of 10 Types of Mushrooms from Retail Suppliers in the United States. While this does show that mushrooms have vitamin D, I’d call the levels of vitamin d in most mushrooms ‘detectable’ rather than being a ‘good source’. Interestingly, mushrooms have an interesting ability to make Vitamin D from sunlight (UV light), just as humans do. I’ll go over why this is important later.
But first, lets go over the study, none of which I question, and am taking at face value. The main part of the abstract in the study is this, “Vitamin D2 was low (0.1–0.3 μg/100 g) in Agaricus bisporus(white button, crimini, portabella) and enoki, moderate in shiitake and oyster (0.4–0.7 μg/100 g), and high in morel, chanterelle, maitake (5.2–28.1 μg/100 g) and UV-treated portabella (3.4–20.9 μg/100 g), with significant variability among composites for some types”.
First of all, they distinguish between mushrooms exposed to UV light exposed mushrooms, (both artificially and naturally in the wild) and those not exposed to UV light (most commercial varieties). This is important because mushrooms do not ‘inherently’ have vitamin d in them, it’s an ‘incidental’ nutrient that is not a necessary quality of ‘mushroomness’ that only occurs upon exposure to UV light. And mushrooms do not need UV light. In fact, they can be grown in complete darkness, and they will do just fine. However, in nature, wild mushrooms are often exposed to some sunlight, and thus end up producing some Vitamin D, hence the difference in the vitamin D content of wild mushrooms and of cultivated mushrooms.
Vitamin D Content of Mushrooms
The cultivated mushrooms in the study contained 0.1–0.3 μg of vitamin d per 100 grams. The symbol of μg stands for ‘micrograms, and is a measurement of vitamin D. But most sources measure vitamin D in IU’s, so we’ll convert it. The conversion from micrograms to IU’s is 40 IU’s = 1 mcg. This conversion means that the cultivated mushrooms contain 4-12 IU’s of Vitamin D per 100 grams. The next thing to take into consideration is that the reason the study reports this in 100 gram weight is that this is a ‘standard’ for reporting nutritional information so that one can compare ‘apples to apples’, so to speak; but it’s not necessarily a ‘serving’.
100 grams is about 3.5 ounces which, in the case of hamburger, for instance, is just short of the amount in a quarter pound burger patty, which is 4 ounces. In the case of mushrooms, a large portabella mushroom cap, the kind used for making ‘faux’ hamburger patties, is about the same size as a quarter pound burger as well. So, it takes a full ‘quarter pound burger’ size of mushrooms in order to get a maximum of 12 IU’s of Vitamin D.
How Much Vitamin D Do You Need
I go into detail about the numbers I use on my Vitamin D Requirements page, but the RDA is about 400 IU’s, while researchers are recommending around 4000 IU’s as the average number needed for the prevention of most diseases, including those outlined on the Symptoms of Vitamin D Deficiency page. To meet even the BARE minimum of vitamin D that is only good for preventing rickets, and is the amount recommended for newborn infants, you’d need to eat between 20-100 quarter-pound burger-sized mushroom caps every day, depending upon the Vitamin D content of the mushrooms! For meaningful disease prevention, you’d need to eat 100 burger-sized mushrooms a day.
Mushrooms Produce the Wrong Kind of Vitamin D
Notice that the study states the mushrooms produced Vitamin D2. Unfortunately, mushrooms only produce the ‘wrong’ kind of Vitamin D for disease-prevention, and it’s the same kind as Vitamin D Enriched Foods as well. If you read on my Vitamin D3 page, you’ll see humans produce and use Vitamin D3 and not Vitamin D2. While Vitamin D2 does increase blood levels of Vitamin D, it simply does not provide the disease prevention of Vitamin D3. Some researchers claim that Vitamin D3 is not fit for human consumption. Even if you did eat those 100 quarter-pound sized mushroom patties, you’d not be getting the right kind of Vitamin D required for disease prevention anyway. So, as you can see, cultivated mushrooms are a poor source of Vitamin D.
What about Wild Ones?
Are Those Mushrooms a Poor Source of Vitamin D?
The study showed that the highest Vitamin D Content mushrooms provided 5.2–28.1 μg of Vitamin D per 100 g. This is significantly more, and converts to about 200-1100 IU’s per 100 grams. Now we’re talking! That’s a decent amount of Vitamin D. However, that still means that you’ll need to get two burger-sized amount of WILD mushrooms every day, just to get the minimum amount for a newborn infant. For meaningful disease prevention, you’ll need to eat between 4 and 20 of those burger-sized patties. Surprisingly, one study on using UV treated mushrooms as a food source showed that the vitamin D2 levels in the blood increased, as would be expected, however, vitamin D3 levels in the blood DECREASED, so that total vitamin D levels did not increase at all despite eating the ‘fortified’ mushrooms! (1)
Additionally, each 100 grams of wild mushrooms are going to be a pretty penny. Online, I found Wild Mushrooms Online for about $50 for 3 pounds. That’s about $3.5 per 100 grams. In order to meet your Vitamin D requirements through wild mushrooms, you’ll be spending between $22 and $220 a day to meet your vitamin D needs, or you’ll have to forage them yourselves, and that is both seasonal and not guaranteed. You’ll also be getting your Vitamin D in the inferior form of Vitamin D2 anyway. It seems completely unrealistic to use mushrooms as any sort of vitamin D source.
However, you’re still not guaranteed ANY vitamin D from those wild mushrooms. It all depends upon if they were exposed to UV light or not, and unless they were held in a facility where they intentionally use UV lighting to enrich the mushrooms, or you do it yourself (you can sun dry your mushrooms for that effect), there is no way to know if there is any vitamin D in the mushrooms you are buying or foraging. In fact, there are two studies on mushrooms that were done with the intent of determining the nutritional content of the wild mushrooms in particular areas of the world, and neither study reports any vitamin D being present.(1)(2)(3) All in all, mushrooms are a poor source of vitamin D. So, don’t believe the nonsense on these sites that claim mushrooms are a good source of vitamin D. They aren’t.