I don't think MP posts come even close to the number of posts about supplementing vitamin D here.
Vit D was named vitamin like when, 60 years ago? but in reality it is a secosteroid hormone:
The bad news for those who are really sick and keep applying the D hormone therapy on themselves is that their condition almost always directly comes from the pathogens shutting down immune activation properties of this hormone, leaving its steroidal/anti-inflammatory part intact, so temporal correction of low levels of D just brings no more than an extra palliation effect to them(with the eventual relapse).
More and more scientific papers shed the light on the pathways pathogens use to persist within the cells. Here is one of the examples, the latest paper on how M. leprae shuts down D mediated immunity:
Upon infection of monocytes with M. leprae, there was no upregulation of CYP27B1 nor its enzymatic activity converting the inactive prohormone form of vitamin D (25-hydroxyvitamin D) to the bioactive form (1,25α-dihydroxyvitamin D)