Vitamin D is one of the oldest hormones we know of. Plants and fungi make vitamin D2 , also called Ergocalciferol. It is similar to our vitamin D and probably older but it is not what we make on our skin! We make D3, Cholecalciferol. In fact, insects, fish, birds, reptiles and mammals all make D3! Animals that are nocturnal, that go out only at night and are never exposed to the sun, still need vitamin D. In order to be nocturnal their bodies must be completely OK with using the vitamin D2 they get from plants. Rats and mice can use D2, and D2 was the first vitamin D that was discovered. Animals that are nocturnal predators rely on the D3 made and stored by the animals that they kill and eat. When we ate the entire animal raw we also benefited from this source, but now that we eat cooked meat we get very little D3 from food. For most of us who are awake in the day and sleep at night the D has always been made on our skin, from the sun. When I first started suggesting vitamin D to my patients, and didn’t know any better, I gave prescription strength D2 once a week because that is what is still “recommended” in the medical literature. But I soon found out that 9/10 of the patients I gave it to didn’t like it, their sleep was worse, they had more belly complaints and more pain. My other patients taking D3 were doing better. Finally I read the articles describing that these are definitely not the same chemical, they are absolutely not equivalent, even in their bone effects.
Vitamin D does actually exist in our bodies as vitamin D3 25OH just as it is supplied in pill form. Most of this form is concentrated in the liver. Sea animals such as dolphins, who have no hair or scales but are habitually under water probably get some D3 made on their skin but also get D3 from the animals they eat. Dolphins and other predators eat the entire animal raw, which we rarely do now. Aboriginal peoples such as the Inuit or Eskimo who had dark skin despite living at very high latitudes probably lived on the D3 they obtained from raw seal, whale or polar bear liver. The habitual eating of raw liver is one of the ways that humans were able inhabit areas where their skin color did not match the sun exposure. Therefore in some specific areas, changes in the diet have definitely contributed to vitamin D deficiency.
Cod Liver Oil:
Be wary of taking vitamin D in the form of cod liver oil. It was the first supplemental source, and you’ll notice the word liver in there. But if you are trying to use vitamin D to make your sleep perfect in order to heal your body you’re doing something a little different than “living a natural life”. Cod liver oil cannot guarantee the dose of vitamin D in each serving because it varies from fish to fish and bottle to bottle. There is so much that is still unknown about vitamin D and getting the D blood level to be stable over time is so difficult, that easy access to cheap consistently dosed pills is one of the few advantages we have today. So use the pills instead so you know exactly what dose you are taking every day.