B12; it's a multifaceted issue, and a very important one for the following reasons. B12 is meant to be made in the intestines, but for many people, that isn't happening, at least not as much as it needs to. And when looking at this issue, we need to keep in mind that, for many people, our needs are higher today than they were many millennia ago, so our body may not be able to provide all the B12 that some people need. Back then, we handled stress like zebras and not like we do today, and stress is a big customer of B12. When a lion jumps into a pack of zebras, chases them, and downs one, the rest of the zebras then stop running and continue grazing as if nothing had happened (they know they having nothing to fear from that lion for the rest of the day). And they don't go around stressed out about the event for the rest of the day either. They "let it go". Humans on the other hand tend to hang on to stressful events, and in our modern culture, there are more potential stressors than at any time in our history, and we tend to accept these stressors as a normal part of living, but we were never designed with such stress in mind.
These "Supply and Demand" factors are enough to account for lots of B12 insufficiencies. And just because you don't have a full-blown B12 deficiency as demonstrated by noticeable symptoms doesn't mean you aren't being adversely affected by a B12 insufficiency.
Then factor in the secondary issues, like not enough of B12's companion nutrients: iodine, selenium, cobalt (the list is long), and there is also less than stellar methylation cycles (which can be affected by genetic factors). So it's no wonder lots of folks are B12 insufficient to some degree.
But those contributing factors are physical ones. Is there anything non-physical that can turn a B12 insufficiency into a deficiency? Yes! Intellectual misinformation such as, "You don't need to test your B12...just wait until you get symptoms," and "If you do have a B12 insufficiency, fasting will resolve it", and other equally bad advice.
And then there are those who focus on B12 to the exclusion of the other equally important nutrients. They feel "off", they take some B12, they feel much better, and they assume "That was it!!!" and there ends their focus on resolving nutrient inadequacies even though they have a few others that need discovering (a low fat diet that is too low in fat can result in an EFA insufficiency which is not good for the brain, and even the healthiest of the raw food diets may contain foods grown in nutritionally inadequate soils because the agri-based food industry is a for-profit industry not a for-nutrition industry). Wholistic approaches should apply to nutrition as well as to any other aspect of health. And when you realize that "Food matters, but nutrition matters too", you'll add another tool to your health creation toolbox. And assuming you want the best health your DNA will allow, this is a good tool to wield.
To properly test B12 status, the Methylmalonic Acid (MMA) test is available from most doctors, and can also be done at home (urine test) and mailed to a lab even from other countries (a resource for this appears in my detailed B12 article... if you're wondering why I don't simply supply you with the resource in this article, it's because you need to know how to properly assess your B12 status, interpret the lab results, and what to do about any corrective measures). If the doctor needs justification to order this "special" test, just explain that the reason you want the MMA test (either instead of or in addition to the standard B12 blood test) is because you consume a goodly amount of dried sea veggies (kelp, dulse), and since the drying process turns active B12 into inactive B12 analogs which would be picked up by the B12 blood test but not contribute to the body's B12 needs, the MMA test is a better indicator of actual B12 status. If this doesn't convince the doc to order the MMA test, hand him/her a note that says, "I will now scream at the top of my lungs until you agree to do the MMA test." Or find a better doctor, or do the test yourself.
Re: swallowed B12 and injections: Swallowed B12 is not the best delivery method because it may not work well enough. Sublingual (under-the-tongue) B12 is best for 99.9% of people. And injections are great for dire emergencies but are not needed otherwise; don't pierce your skin unless absolutely necessary (says a surgeon acquaintance of mine).
BOTTOM LINE: Test! And not with the standard B12 blood
test, please. MMA, as either uMMA or sMMA, is the "Gold Standard"
test for B12 status assessment (notice I didn't say B12 level assessment).
Don't guess or assume... test. And test before you get symptoms
to avoid getting them and the damage that comes along with them. Your
future health depends on you making wise decisions today.