B12 Deficiency and Pernicious Anemia

Pernicious anemia is a macrocytic (larger than normal RBC) and megaloblastic (immature, abnormal RBC progenitors in the bone marrow) anemia. Pernicious anemia is caused by a deficiency of vitamin B12 (Cobalamin). Generally, vitamin B12 deficiency occurs due to lack of Intrinsic Factor – IF. Intrinsic Factor is a glycoprotein in the gastric juice that is necessary for the absorption of dietary Vitamin B12. It is very rare that B12 deficiency occurs due to lack of dietary intake because of it is wide spread occurrence in all animal foods and synthesis by intestinal flora.

Intrinsic Factor is secreted by parietal cells of gastric glands. It helps in the absorption of B12 by binding it tightly. In the bound state the B12 is protected from digestion by the gastrointestinal enzymes. In the bound state the Intrinsic Factor binds to specific receptor sites on the brush border membranes of the mucosal cells in the Ileum. Finally B12 is transported in to the blood by the process of pinocytosis carrying the Intrinsic factor and the vitamin B12 together through the membrane.

Once B12 has been absorbed from the gastrointestinal tract it is stored in large quantities in the liver & then released slowly as needed to the bone marrow and other tissues of the body .The total amount of vitamin B12 required each day to maintain normal red cells maturation is about 5 micrograms and the normal store in the liver and other body tissues is about 1000 times this amount . Therefore as many as 4 to 5 years of defective B12 absorption are required to cause Pernicious anemia.

Deficiency of vitamin B12 can result in a deficiency of Folic Acid by causing the entrapment of Folate as 5-methyltetrahydrofolate. The methyl group of 5-methyltetrahydrofolate is transferred to Cobalamin (B12) to form Methyl Cobalamine and the folate is returned to the folate pool to further take part in one carbon transfer reactions . In case of deficiency of B12 folate remain trapped with the methyl group it’s further functioning is impaired.

Due to B12 & folic acid inter related roles in the protein synthesis a deficiency of either B12 or Folic Acid will result in megaloblastic anemia. However in B12 deficiency there is an impairment of microbicidal activity of leukocytes .The function of leukocytes is not impaired in Folic acid deficiency. Also due to B12 deficiency gastrointestinal tract, peripheral & nervous system are also affected .Numbness & tingling in the hands & feet, poor muscular coordination, poor memory & hallucinations are some symptoms of B12 deficiency. If the deficiency continues long enough, the nervous system damage may be irreversible even with treatment.

Nutritional Care in Pernicious Anemia:

A high protein diet (1.5 Gm/Kg of body weight) is desirable. Green leafy vegetables should be included in diet. In non vegetarian food items, liver is the richest source of vitamin B12 so it should be included in diet. Beef and pork, eggs, milk and milk products are good sources of vitamin B12, although the cholesterol content should be considered.

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