Vitamin B12 is naturally found in animal products, including fish, meat, poultry, eggs, milk, and milk products. This is why vegetarians and vegans are at greater risk of not meeting recommended levels of vitamin B12 in their diet.
It is generally not present in plant foods, but fortified breakfast cereals provide a non-food-bound source of vitamin B12 with high bioavailability. This is important for vegetarians, vegans, older adults with inadequate stomach acid, or those who regularly utilize antacids.