Vegetarians who do not eat meats, fish, eggs, milk or milk products, or B12 fortified foods consume no vitamin B12 and are at high risk of developing a deficiency of vitamin B12 . When adults adopt a vegetarian diet, deficiency symptoms can be slow to appear because it usually takes years to deplete normal body stores of B12. However, severe symptoms of B12 deficiency, most often featuring poor neurological development, can show up quickly in children and breast-fed infants of women who follow a strict vegetarian diet.

Fortified cereals are one of the few plant food sources of vitamin B12, and are an important dietary source of B12 for vegetarians who consume no eggs, milk or milk products. Vegetarian adults who do not consume plant foods fortified with vitamin B12 need to consider taking a B12-containing supplement. Vegetarian mothers should consult with a pediatrician regarding appropriate vitamin B12 supplementation for their infants and children.