Humans obtain vitamin D from diet and sunlight. There are two main forms of vitamin D: cholecalciferol (vitamin D3) and ergocalciferol (vitamin D2). The main source of vitamin D3 is from exposure to sunlight, which accounts for more than 90% of the body’s vitamin D requirement. Vitamin D3 is synthesized in the human skin by a photochemical conversion via ultraviolet B (UVB) exposure of provitamin D3 (7-dehydrocholesterol). Vitamin D2 is sourced from the UV irradiation of ergosterol, which is a steroid found in some plants but largely fungi. Humans have a combination of vitamin D3 and vitamin D2 available to them from sunlight UV exposure (vitamin D3), egg yolks and oily fish (vitamin D3), fortified margarine, milk and breakfast cereals (fortified vitamin D2) and dietary supplements (vitamin D2 and vitamin D3).
Both vitamin D2 and vitamin D3 undergo similar enzymatic hydroxylation processes which converts them to the active metabolite 1,25-dihydroxyvitamin D2 or D3 (calcitriol). The liver and kidneys participate to make this active form of the vitamin that the body can use. However, there may be differences in their respective efficacies in raising serum 25(OH)D, which is a marker of vitamin D status. Differences may be due to their differing affinities for the vitamin D receptor. It is also thought that vitamin D3 is the preferred substrate for hepatic 25-hydroxylase.
Some studies indicate that vitamin D3 is more efficacious at raising serum 25(OH)D concentrations than is vitamin D2; and that vitamin D2 is 30% to 50% less effective than vitamin D3 in maintaining serum 25(OH)D levels. However, other studies have
suggested that both forms of vitamin D are similarly effective.
On EVCLO and vitamins:
One of the main reasons cod liver oil from the Atlantic Cod is so healing is due the high
levels of vitamin A and vitamin D3 in a healthy ratio along with significant levels of
Omega 3 DHA/EPA. No other fish species including other species of cod contain these
levels of vitamins. Alaska Cod and Alaska Pollock for example are both related to
Atlantic Cod. They contain mid-range levels of vitamin A and very little vitamin D3.
This article applies to: Rosita Extra-Virgin Cod Liver Oil (EVCLO).