In many deficiency-related diseases doctors prescribe to supplement, that which is deficient. For example, if insulin is found deficient they replace with insulin. Similarly the case with vitamin deficiencies, calcium deficiency, thyroid deficiency etc. I have a few doubts on this regard, 1) Have they ever try to ascertain why such deficiencies have occurred? How long can one keep on supplementing them? Why the cause of deficiency is never found out and treated? 2) Has it ever occurred to them that this kind of deficiencies could have been the body's way of adaptation to deal with something else? It could have been a temporary armour against something. For example, it is found that the body intentionally brings down the iron level during fever. There may be some advantage to it. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3938201/ If so, supplementing deficient items may prove detrimental too. Unless the cause is analyzed, we can't blindly supplement. So I'd it right to supplement the deficiencies blindly? Is there any rationale behind my doubts?