the body has many of these type of scenarios in its mechanism to regulate hormones and other chemicals
basically there is often a storage form and an active form - and enzymes convert one to the other locally as needed by conditions
the big variable that dysregulates this is inflammation - ie chronic activation and dysregulation of the immune system
when inflammation is low ( the normal state for healthy humans long term) - things work as intended - 1 form is correctly converted to the other in the right amounts to maintain homeostasis - and all is well
when its high - the opposite pathway is activated and too much of the wrong type is made or built up by not being used
so inflammation is the real more root cause issue - which is driving the vitamin D issue - which is why LDN may help to some degree ( one property of LDN is to reduce inflammation)
vitamin D is classified as a vitamin only because there is a stereotypical disease state that occurs due to extreme deficiency ( the original definition of a Vitamin ) but its actually an important hormone which involved in many many processes in the body - including immune function.
related to this there is a somewhat fringe but fairly well known theory of chronic illness - especially auto-immune diseases and chronic lyme etc - called the Vitamin D hypothesis - by a Dr Marshall
he believed that we are curranty chronically overdosed with Vitamin D through fortified foodstuffs - and if one can restrict all vitamin D from diet and sunlight - the body will somehow reset by using up the storage form and resensitising itself to the proper form.
his website here
https://mpkb.org/home/patients/pathogenesis_overviewfrom what i can gather there are reports of some patients who have had some success with his protocols (which do also include antimicrobials) - but they seem to be in the minority and most find it too arduous.
alternately - according to more mainstream sources on chronic lyme - chronic lyme patients are often low in vitamin D and supplementation is advised - low vitamin D is also associated with immune dysregulation and auto-immune disease
essentially there is debate about
the directionality of the arrow of causality in the associations between between inflammation and vitamin D status