[telchior]

Yep. I didn't mention it but with magnesium testing, blood tests may not catch an issue; you can be deficient in a particular organ (e.g. brain) and fine in others.

But realistically, very little of the $100 billion+ supplement industry is built on anything medically necessary. Yes, I have a waste basket diagnosis with an unclear cause that's helped by a specific supplement, but there are quite literally dozens (perhaps even hundreds) of other supplements that the snake oil merchants swear up and down are essential for the same condition, and they'd happily claim that whatever deficiency exists is undetectable. That's why I "don't believe" in supplements in general.