My understanding is that if we're supplementing with Vitamin D, then D3 is a better choice than D2. (Also: http://heartscanblog.blogspot.com/2007/04/vitamin-d2-vs-vitamin-d3.html)
So I was surprised to learn that from some samples of Green Pasture's Fermented Cod Liver Oil, the "majority of D is D2."
I realize that the Vitamin D content of fermented cod liver oil is only one of the reasons to take it (others being for e.g. A, K2 and E, as well as omega 3). And so I wouldn't necessarily not take it because of its D2 content. Although I did read somewhere that it's much easier to overdose on Vitamin D2 than D3.
However, I am looking for natural / whole food sources of Vitamin D3, and am wondering, if that's one of my top reasons for taking Fermented Cod Liver Oil, should I reconsider?
I'm also thinking that there's so much we still don't know about Vitamin D - is it possible that D2 taken in this natural form is somehow better than D3 taken as a standalone supplement?
Edited to update:
I asked a slight variation of this question on Chris Masterjohn's blog post at WAPF about vitamin D.
For the fermented cod liver oil that WAPF recommends, what do you make of the majority of vitamin D being D2? (http://www.greenpasture.org/re...=test-data)
My understanding is that it's D3 that we should be supplementing with?
Also, I've read that D3 is found in animal sources whereas D2 comes from plants? So where does such a high level of vitamin D come from in the cod liver oil? I try to eat natural / whole food sources of vitamins rather than supplements, which is why I like the idea of cod liver oil - I was just surprised about the D2 and am trying to get a better understanding.
Here is his answer:
I don't know the answer and I think there are many unresolved questions about the vitamin D's in marine oils. Obviously it's false that D2 comes from plants and D3 from animals, as fish are animals (though this may be accumulated from plankton or other non-animal sources). I think it's important to realize that we don't know the biochemistry as much as the hysteria-driven vitamin D movement maintains that we do, and therefore we should look at clinical effects of foods, and not try to extrapolate from specific chemical forms in foods or rely too heavily on 25(OH)D levels in and of themselves.
I definitely agree that there's a lot we still don't know (and I appreciate Chris' response).. still hoping to get some more insight..
Vitamin D is the main reason that I take Green Pastures FCLO as well (I'm evening shift and am lucky to even see the sun for more than 15 minutes a day let alone be in it).
It seems strange to me that there would be so much D2 in the FCLO. It was my understanding that D2 is mainly from plants and D3 is mainly from animals. The steady increase of D2 on that chart combined with the steady decrease of overall D is a bit worrying to me. Something has always seemed just a tiny bit off to me about that company, and it makes me wonder if they're starting to compromise quality to meet demand. I do feel better on their CLO than I have on other brands, but it is worrying.
As for whole food sources of D3, this is all that I've managed to find with a bit of Googling.
"D3 is present in all animal produce because it is in all animal tissues, although not everywhere in large amount. We eat fish, butter, lard, suet, cream, cheese, meat, organ meat (livers, hearts, kidneys, poultry skin, tongues, tendons etc). We render our own pork fat out of pork bellies (mince and leave in a slow cooker for 8h). Animal fat contains D3." from WebMD.
And: "D1 is produced by humans upon exposure to sunlight; D2 (ergocalciferol) is made from plants or yeast, D3 (cholecalciferol comes from fish liver oils or lanolin" from a page that seems to be afraid of animal products.
Vitamin D2 (ergocalciferol) is produced from ergosterol in fungi or yeast by irradiating it with ultraviolet light. I have not heard of it occuring naturally in fish.
I would be curious to know why high levels of vitamin D2 in the cod liver oil if the producers are not adding it themselves.
I thought to add this information from usda nutrition database:
Fish, cod, Atlantic, raw
Vitamin D (D2 + D3) mcg 0.9 1 0.000
Vitamin D3 (cholecalciferol) mcg 0.9 1 0.000
Fish, cod, Pacific, raw
Vitamin D (D2 + D3) mcg 0.5 4 0.123
Vitamin D3 (cholecalciferol) mcg 0.5 4 0.123
So in cod flesh, according to this, no D2.
I also checked cod liver oil entry there, and it had pretty round numbers, 250 mcg D2+D3 and 10000 IU D3, which works to zero D2, but I suppose those are just added vitamins and may not be based on actual analysis of the cod liver oil.
There are also other entries of fish liver in in the database, but unfortunately no D2/D3 sections. Also no D2/D3 information about sea mammal livers, if that's relevant.