The adult human only needs 2.4 micrograms of B12 per day and it is stored in the body. (1,000 micrograms equals one gram) Thus, a vegan could take supplements or simply eat one egg or cheese meal per month or so and get all the B12 they need.notself wrote: B12 only comes from animal products. Butter, milk and eggs all contain B12
There are some vegan sources (in limited amounts) that have B12 too, including tempeh, miso, sea vegetables, and nutritional yeast.
For lacto-ovo (dairy and eggs) vegetarians it is not an issue and they consume more than enough of B12 and other nutrients, with a balanced, healthy diet (limited amounts of junk food).