An analogy would be the analysis of car exhaust, finding certain levels of CO2, and trying to fix cars with "bad exhaust" by throwing more CO2 into the intake (except maybe this would even have a negative effect by hindering combustion).
This is an hilarious (and fitting) analogy for nutrition sciences.
Reputed and trustworthy citations from scientific sources required, please.
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".
"Gravity is real."
"Reputed and trustworthy citations from scientific sources required, please."
You can get less and less ridiculous from here ad nauseam, but the point is made.
https://www.theguardian.com/science/2018/mar/09/is-vitamin-d...
And those studies saying otherwise have been backed by a lot of questionable money: https://www.nytimes.com/2018/08/18/business/vitamin-d-michae...
Oh by the way sunscreen is terrible, it doesn't have a proven link to reducing cancer and it destroys reefs so do yourself a favor and get more sun without all the slimy goop so you can feel better AND save the planet!
Also, the science is starting to question the supplementation. It’s too early to tell, but one hypothesis is that it is a biomarker at the end of a pathway and not at the beginning of it, i.e. as a consequence of a proper diet and sunlight, and not a cause of a healthy system.