Even metabolically innocuous substances can be dangerous in quantities sufficient for violent external application e.g. when being dropped[1] on one's head.
What do we call vitamin D surfeit? Arichitis?
[1] Although non-volatile storage these days is a choking hazard, in the earliest days of computing a couple of megabytes would have been fatal if their cabinet were to fall on someone.
(No lang belta this comment: Belters both have more pressing bone issues from life near the float, and get vitamin supplements from the pastes for their kibble, so unless the Belt somehow has universities somewhere and they're premeds cramming, they have absolutely no concept of rickets.)
Not really sure your point. Are you saying that there is no upper safe limit for B12 for all people?
>...Case details: A young woman was treated with multiple daily doses of 1 mg of cyanocobalamin for severe pernicious anemia. After a total dose of 12 mg, she developed acne, palpitations, anxiety, akathisia, facial ruddiness, headache, and insomnia. She improved two weeks after stopping the drug. There were no sequelae nor complications.Discussion: Although these symptoms of cobalamin toxicity were unexpected and unusual, the case reminds us that the administration of any drug is not entirely safe.
"All things are poison, and nothing is without poison; the dosage alone makes it so a thing is not a poison."