@northoftheborder

It is very important to know that both vitamin B12 deficiency and folate deficiency are more common in older people, affecting around 1 in 10 people aged 75 or over and 1 in 20 people aged 65 to 74.

B12 deficiency can effect body in may ways and can cause major physical, neurological, and psychological health issues because the body needs this vitamin to make red blood cells, build DNA, and protect nerve fibers.

Aging effects correct absorption of B12 - it is diminished even if there is adequate amount of it in our diet. So, if elderly is deficient just taking supplements orally might not resolve the problem and administration by injection is needed and gives much faster results.

And yes, vegan diet should not be implemented without thorough understanding of it, which applies to any kind of a diet (Atkins, Paleo, intermittent fasting , etc etc. )