A recent article in AARP Bulletin discussed the importance of taking vitamin D and vitamin B12 supplements. Concerning B12, the incidence of an autoimmune disease, called pernicious anemia, increases alarmingly as we age. This condition cannot be addressed by dietary supplements, but it is easily diagnosed by blood tests. The loss of ability to absorb B12 through the intestine is addressed by receiving a shot of B12 periodically.
Thanks for pointing out this alternative. I was contrasting dietary supplements (as in an oral pill). The sublingual route is different and clearly effective. I should say, swallowing a B12 tablet won't address pernicious anemia, and incidence of B12 deficiency increases with age.