I had time to do a bit more research and found a few more links of interest. First this which is my favourite way of getting Codliver oil in my diet.
Next I don’t know Chris Kresser but have enormous respect for the The Weston A. Price Foundation whose president’s letter on this subject is quoted on Chris Kresser’s webpage.
As I suspected a lot of codliver oil these days is treated to take the fishiness out and synthetic vitamins added to replace the ones lost. The foundation suggests this is why codliver oil does not have the same good results at treating chest infections as it did in the 1930’s.
They recommend a brand (that I will be purchasing) and give a lot of scientific information about the importance of taking vitamin A and D together from an animal based source.
The brand they recommend is this one Extra Virgin Pure Cod Liver Fish Oil - 150ml | Rosita Real Foods – Rosita USA which looks different than the one at the end of the letter which might be a sponsor of Chris Kressers website.
The The Weston A. Price Foundation letter is here:
Weston A. Price Foundation Clarifies Recent Claims Against Cod Liver Oil
The next link is research which quite alarmingly shows that many vitamin D preparations have a lot more of the vitamin in them than stated. This leading to many serious incidence of toxicity. A couple of deaths even resulting from synthetic vitamin D that was added to commercial milk:
A review of the growing risk of vitamin D toxicity from inappropriate practice - PMC
I am not certain but would suspect that the toxicity cases attributed to fishoil in this report most likely involved fish oil that had added synthetic vitamin D.
The vitamin A and D toxicity saga is one I have been aware of and followed for many years with my father treating many of his patients successfully with Codliver Oil and grass fed butter and always wary of synthetic A and D. He was a respected Obstetrician and not a quack. My beautiful children happily took codliver oil off the spoon growing up. None of them sick for more than a day or two ever and never with chest or ear infections. All too with straight teeth and well formed bones.
Somehow I lost the plot on this in the past 10 years or so and am glad I got back on track. Make your own decisions obviously but I was glad to find the The Weston A. Price Foundation’s recommendations.