Very low B12 intakes can cause anaemia and nervous system damage.
The only reliable vegan sources of B12 are foods fortified with B12 (including some plant milks, some soy products and some breakfast cereals) and B12 supplements. Vitamin B12, whether in supplements, fortified foods, or animal products, comes from micro-organisms.
Most vegans consume enough B12 to avoid anaemia and nervous system damage, but many do not get enough to minimize potential risk of heart disease or pregnancy complications.
To get the full benefit of a vegan diet, vegans should do one of the following:
eat fortified foods two or three times a day to get at least three micrograms (μg or mcg) of B12 a day or
take one B12 supplement daily providing at least 10 micrograms or
take a weekly B12 supplement providing at least 2000 micrograms.
If relying on fortified foods check the labels carefully to make sure you are getting enough B12. For example, if a fortified plant milk contains 1 microgram of B12 per serving then consuming three servings a day will provide adequate vitamin B12. Others may find the use of B12 supplements more convenient and economical.
The less frequently you obtain B12 the more B12 you need to take, as B12 is best absorbed in small amounts. The recommendations above take full account of this. There is no harm in exceeding the recommended amounts or combining more than one option.
personally, i prefer to eat natural B12 in moderation but enough to be healthy and sustain.
If it is a plant, eat it, if it comes from a plant, don't!