1,25
According to dr Marshall, d25 suppresses the immune system by inactivating the
VDR. It is only the 1,25 form that activates the
VDR (= activation of immune system).
http://mpkb.org/home/pathogenesis/vitamind
VDR is downregulated by HIV, tuberculosis and other pathogens because VDR protects the body, so the pathogens found this way to weaken the protection. Taking D3 while already chronically sick (25D low, 1,25D high) actually helps the pathogens and shuts down the immune system.