vitamin B12 is required for the development, myelination, and function of the central nervous system; healthy red blood cell formation; and DNA synthesis, it is essential for bone formation and among other functions. Long-term B12 deficiencies are extremely serious, affect the brain and nervous system function, and can be irreversible.
I’ve heard vegans say that they don’t take B12 and feel fine, but I want to point out that if you’re deficient It can take quite a while to have symptoms of deficiency – So note that you can be deficient for some time without realizing it
B12 is synthesized by certain bacteria, which show up in many places, including the guts of animals, which is why meat is the most well-known source of B12.
The plant-based foods we eat also grow in soil that used to be full of B12-rich bacteria, but that was before the mass commercialization of agriculture before our water was purified with chemicals, and our farmland treated with pesticides, fungicides, and insecticides. And before we scrubbed our fruits and vegetables so thoroughly that they would look better (and last longer) on the shelves of the grocery store, but that they would also be void of any traces of earth, much less vitamin B12.
In fact, more and more omnivores are starting to turn up B12 deficient now for the same reason.
So B12 deficiency is less a symptom of being on a plant-based diet, as it is a consequence of how we have treated the land we farm our foods on.
B12 supplements are also highly recommended for everyone over the age of 60 regardless of whether they are on a plant-based diet or not, because of decreased absorption.
There are some plant-based places you can get B12, like Nutritional Yeast (Nooch) and Marmite fortified foods breakfast cereals, and some plant-based milks, some juices.
The suggested recommended supplement for people on a plant-based diet is 50-250mcg per day or 2000-2500 mcg per week