There’s a lot of that with trace minerals, both in animal and plant biology. I’ve recently heard a bit about trace minerals as an issue in soil fertility.

Lately, I’ve been wondering about zinc… I heard a rumor that zinc deficiency can be associated with anorexia, producing an effect of “food doesn’t taste right”. That would seem eminently testable, especially with the prevalence of zinc lozenges for treatment of colds. Dr. Charles, have you heard anything about that?

Even its use in eclampsia is something akin to voodoo, that is, if voodoo doctors managed to publish their experience in the Journal of Voodoo Medicine. This isn’t to say that it doesn’t work or seem to work, but why it works is unclear, as well as knowing when to stop. It seems you keep giving it until the patient stops doing things you don’t like.

I’m being tongue-in-cheek, but I’d say not so firmly tongue-in-cheek.