I agree the thinking makes since and you can get to your colon faster through your rectum but (no pun intended) I think I will pass on shoving vitamins up my ass..lol
I see injectable vitamins for animals, we as humans get infections easier and injecting vitamins doesn't disperse them like they are supposed to be as the filter through the organs. Its a dangerous way of doing it especially since vitamins are a single bond substance and any attempt to sterilize them would destroy the integrity of the supplement. Its like adding gas to Styrofoam-if you haven't done this do it. It creates a mush but also completely breaks down the substance to a wasted molecular level that no longer suits the original purpose of filtration and breakdown in the body.