Vegetarians, older folk advised to get enough B12
Reuters - Vitamin B12 deficiency is more common than doctors once thought, and experts advise that those most at risk -- vegetarians and older adults -- be sure to take supplemental forms of the vitamin.
What an ironic story to come across! My mother, who is not old (50 something) was told that she was b12 deficient. My father was not low in b12 but was in a couple other b vitamins that are important. Since neither of them have changed their diets, it makes me think that their bodies are not absorbing and using vitamins like they used to. It does make sense that when the body slows down, that other processes like absorbtion also slow down.
Vitamin B-12, and a knockoff version, create complex market for marine vitamins
Vitamin B-12 exists in two different, incompatible forms in the oceans. An organism thought to supply essential vitamin B-12 in the marine environment is actually churning out a knockoff version. Ref. Source 9w.
In this video you can learn about the optimal level for vitamin B12 regardless to if you are eating a plant based diet or not, however if you are a plant based eater then this topic is not optional for you. You will need to ensure proper absorption of the B12 and the B complex on the whole through other sources such as those found in fortified foods and vitamin supplements.