If one is a vegan (a vegetarian taht eats no animal products at at i.e eggs, 
milk, cheese, etc., after about 3 years of a vegan diet, you need to start 
taking B12 supplements because b12 is found only in animals.) Acutally our 
bodies make B12, I think, but our bodies use up our own B12 after 2 or 3 
years.  
Lacto-oveo vegetarians, like myself, still get B12 through milk products 
and eggs, so we don't need supplements.
And If anyone knows more, PLEASE post it.  I'm nearly contridicting myself 
with the mish-mash of knowledge I've gleaned.