I like this company, Green Pastures, very much. We've used their fermented fish oil products for several years. Interesting premise about vitamin D, and would explain why the Eskimo could get enough vitamin D even without much sun.
Food Chain as Orgin of Vitamin D in Fish
"Here are a couple studies that show the prominence of vitamin D in the base of our food chain, grass and plankton. The study of the hormone we call vitamin D is in its infancy. The general conclusion of 'vitamin D is good for me' is a good conclusion but to draw deep meaning, or molecule counting like conclusion, is way too early. (Related study; chytochrome 450, health of the thyroid, age etc..)
"I recall many years ago when I was attempting to understand our products a lab ran a Vitamin D test on our High Vitamin Butter Oil. The results came back with the HPLC graph. Circled on the graph with a hand note from the technician was a notation something like ' very unusual, have never seen this in dairy. Have seen a couple times in different fish oils'. The same type reaction from technicians is noted when testing our FCLO for vitamin D. Many unusual peaks within this graph that are not understood. The first study on the pathway of hormone D in fish was just completed a couple years ago. We are many years away from understanding the foods we eat as it relates to hormone D and how the introduction of D in our diet affects our bodies/health."