There’s a lot more to consider when talking about vitamins and your body.
It isn’t so much your body getting “used” to vitamins, as it is the metabolic processes your body goes through regularly deciding how much, for how long,when, and where to put to use the vitamins and minerals you ingest.
Even if your urine has a yellowish tint or is a hue darker doesn’t always means the vitamins have anything to do with it. It could be reactions to medication, your metabolism, stress, what you’ve eaten that day, how much sleep you did or did not get, and sometimes it can very well be caused by too many vitamins and minerals or a lacktherof.
No you won’t experience hair loss, or any growth regression. Your body, hair, and vitamins have a bit more varying and somewhat complex relationship than that.
It’s of more influence to brush up on metabolic processes to further understand how minerals and vitamins play a role in hair growth. They aren’t the only or even main triggers of it, and while they can effect it, they more or less supplement it. Your hair in general, is a byproduct of what your body does after it’s metabolized keratin, amino acids, and a few more minerals I can remember at this moment. From what I understand in past studies I had been assigned concerning metabolism and energy production, it’s mostly a matter of how efficient your body is at handling energy, in whatever form it’s been received. Which is why a lot of studies have linked metabolism with hair growth, hair loss, and genetic traits concerning length, graying, and scalp health/issues. While your body has different metabolic categories concerning metabolism, and your cells and protein functions have their own specific genetic sets of instructions, they are still influenced by energy output and input, and your overall metabolism concerning your body as a single working unit.
While there’s a lot more specific and in depth explanations on stuff like this, I just gave a very generalized sum of things. Which I probably shouldn’t do, concerning accuracy, but I don’t think it’ll hurt anything.
Tying this in with vitamin supplementation is dependent on the metabolic functions your body carries out. Your progression doesn’t always have to stagnate or regulate. If you play around enough and examine any feedback you get from your body or your hair and continue to tweak and adjust if you need to, you can still increase growth rate. I’m not sure for how long though. And that’s dependent on you and your personal life, and/or preferences for how you take care of yourself and your hair.