Every cholecalciferol molecule is the same. This is chemistry. Chemicals that are not the same cannot have the same chemical name. Every animal (without a ge

Every cholecalciferol molecule is the same. This is chemistry. Chemicals that are not the same cannot have the same chemical name. Every animal (without a genetic defect specific to the precursor chemicals) produces the same 7-dehydrocholesterol molecules, and every 7-dehydrocholesterol will, under UVB light, convert to cholecalciferol. Industrial production of vitamin D3 irradiates the 7-dehydrocholesterol extracted from sheep's lanolin with UVB light. There is some question as to whether ergocalciferol--a chemical mainly found in fungi that produce ergosterol and have been exposed to UVB light--is biologically equivalent to cholecalciferol in humans. It can alleviate vitamin D deficiency symptoms, but it is not known with certainty whether it can produce a sufficiency. As far as I am aware, the known cases of hypervitaminosis D have resulted from ergocalciferol supplementation, rather than from cholecalciferol. If you are supplementing with vitamin D3, the chemical you are consuming is identical to that produced in your skin under UVB irradiation. There is no evidence whatsoever that it is destroyed in or poorly absorbed by the human digestive system. If you swallow 15000 IU of vitamin D3, that is the equivalent of standing shirtless in temperate midday sun for 15 minutes, after which time you will achieve no further benefit until some time has been spent absorbing the cholecalciferol and replenishing the 7-dehydrocholesterol in your skin. It is poorly known, that if you have to preface a statement with "it is well known", what follows is less likely to be "known" than "unattributably rumored".