@GorgyS - it is interesting that one of the links suggests (as @Fraser said) that PN may be caused by a lack of Vit B6 .... and it well may be.
But as with any meds, taking the correct dose is critical - and it looks like the overdoses are all accidental thru not knowing what's in the tablets/supplements that they're taking ... even a Doctor who has had quite debilitating side effects from accidentally taking too much.
Even arsenic (in tiny amounts) was used as a beauty aid back in the 1800s (it made the skin beautiful & pale & translucent ...) But take too much - and you're dead!!
