Vitamin B12 is found naturally in a variety of animal products, including meat, fish, poultry, milk, eggs and dairy products, according to the National Institutes of Health. In addition, fortified breakfast cereals are a great dietary source of Vitamin B12.
Vitamin B12 works to help the body produce red blood cells and DNA, among other functions. The recommended dietary allowance of Vitamin B12 for healthy individuals age 14 and over, including both males and females, is 2.4 micrograms. Pregnant women need slightly more Vitamin B12 (2.6 mcg) and lactating women need even more (2.8 mcg), according to the NIH.
Vitamin B12 deficiency can be caused by a variety of conditions, including atrophic gastritis, which is caused by thinning in the stomach lining. Pernicious anemia , Crohn's disease, bacterial growth, celiac disease and parasitic infection can also cause depletion of Vitamin B12. Surgery, including weight loss surgery, can result in Vitamin B12 deficiency, as can disorders of the immune system such as lupus and Graves' disease. Chronic use of acid-reducing medications can also deplete the body's stores of Vitamin B12, according to WebMD.
Because vegans do not eat animal products, cheese, milk or eggs, they are at special risk for Vitamin B12 deficiency, warns WebMD.