Data in this node is out of date. While is is highly debatable how much B12 is needed to remain healthy, it is clear that the amount varies highly from person to person, and that some tests traditionally used for measuring B12 do not accurately measure the B12 accessible for use by our bodies. It is becoming widely recognized that the current recommended daily allowance is too low.
IANAD, but it is safe to recommend a minimum daily intake of 10 micrograms a day. Vegans, vegetarians, and partial-vegetarians should take a supplement; while your body does store some B12, this stored B12 is not available for all necessary functions, and small but measurable ill-effects become apparent within a few months of beginning a reduced meat and/or dairy diet.
Please be aware that the majority of information you see on the internet is well out of date, and is often incorrect. Unfortunately, this is also true of the information given by many doctors.
It is important to remember that you body cannot use all types of B12. B12 from plant sources are highly unreliable, and it is probable that your body cannot use the B12 analogs that are often advertised from soy products and other vegetable sources; it is much more likely that these will inhibit your uptake of the forms of B12 that your body needs.
-- Tem42