the reason i am suggesting the shots is because you dont know how much youre absorbing. the shots are the sure way to find out because they are a sure way to get it absorbed. most people dont absorb it well. others have parasites that rob them of it. but mainly, its the slow decline and inability to replenish which is the problem.
injectable B-12 allows you to absorb all those other trace metals that you need but cant get without B-12.
i believe there are mechanisms in our environment which prevent us getting enough B-12. as with iodine supplementing, its fighting fire with fire, directly at the source. i dont like recommending shots, i think they are critical, at least until you get a handle on it. i have a lot less stress in my life because of it.