I know the 'set point' theories are debated, but many people certainly find that they tend to hang around a certain weight, or hit weight loss plateaus. This can be due to a lot of things...
What about something like testosterone levels? If someone has low-normal testosterone levels, and they supplement to bring them up to high-normal, what happens in the body to down-regulate endogenous production and thus require higher dosages to maintain the same effect?
Hormones are the slow acting system that affects the Sterol binding site. Eicosanoids are the fast acting system that determines your hormone panel. Both are directly tied to the settings on your epi genetic switches. Inflammatory cytokines are what control those switches. It is a very dynamic system and acts like knobs on a equalizer. Adjusting one does not give the context or the 1 to 1 move others. So the answer is no......they do not have set points because they have evolved to be quite dynamic. Sometimes we need low levels and other time supraphysiologic levels can help. Your point of view must encompass both the well and fit person and the person who is not. The therapeutic index of the not well person is quite different than the person who is well. Context matters here big time.
I'm not entirely sure what you're asking... but my body doesn't produce enough testosterone, so I inject it each week. I take blood tests every once in a while and if the results are in "normal male range" I continue the same dose, but if they are too high I'm told to lower the dose because eventually too much testosterone is apparently converted into estrogen. I've done this for one year, I will have to for the rest of my life, when I find the correct dose (it was high the last test I had) I will keep that dose for the rest of my life. Hope that gives some perspective.