IT IS THE MOST STABLE AND WIDELY USED FORM OF VIT AND HAS HAEMATOPOIETIC ACTIVITY APPARENTLY IDENTICAL TO ANTIANEMIC FACTOR IN PURIFIED LIVER EXTRACT. IT ACTS AS COENZYME IN NUCLEIC ACID SYNTHESIS. ITS DEFICIENCY MAY OCCUR IN STRICT VEGETARIANS. FOR ADULTS A DAILY REQUIREMENT IS 1-2 MICRO GRAM WHICH IS PRESENT IN MOST NORMAL DIETS. VIT B12 OCCUR ONLY IN ANIMAL PRODUCTS.MEATS,LIVER,KIDNEYS,MILK,EGGS AND OTHER DAIRY PRODUCTS ARE RICH SOURCES OF VIT B12.IT IS SYNTHESIZED PURELY BY MICRO-ORGANISMS