Let me look around, but you are very right in that finding the kind of information you are looking for is difficult. The manufacturers are not required to do studies to prove safety and efficacy and that are then independently reviewed. So what I have found is that I'll see them claim that clinical studies showed X, but what I find is just their propoganda, not the information in a peer reviewed journal.

There are things that I know have been shown to have the same kinetics when given intransally as given orally, so that isn't out of the question. But whether that holds true for B12 and D, I don't know. But I'll search around and see what I can find.

Of course one option is for you to be your own study with an N of 1. Try the nasal spray and then get retested and see if you are still deficient. If not, then for you, this works.

OK - just found a couple reports of sustained blood levels of B12 with intranasal administration. The study was done to compare intramuscular administration, which is what you would do for pernicious anemia, with intranasal.

Not finding the same for Vitamin D though, in fact one abstract that isn't letting me get to the whole article even though I think it should, is saying it is best taken orally.

But your instinct that perhaps the information you seek is not out there, is probably right. I will keep looking though. Did you ask the dr that diagnosed you as deficient? Though they probably won't have the answer either.