Pernicious anemia is caused by a deficiency of vitamin B 12. It would show up on a blood test because of the large immature red blood cells that are present. These large red blood cells are very inefficient at carrying oxygen.
It can have at least 2 causes – one a lack of vitamin B 12 rich foods in the diet – two an inadequate amount of the intrinsic factor in the stomach. People at risk for pernicious anemia are vegetarians unless they have a high intake of folacin which helps red blood cells develop to the correct size and shape. However adequate folacin does not repair the nerve damage caused by a vitamin B 12 deficiency.
Actually, it can take quite long, up to 5 years, to develop a vitamin B 12 deficiency depending on a person’s body stores. The amount of vitamin B 12 your body stores is dependent on the amount of vitamin B 12 rich foods you eat. Animal products are the best source of vitamin B 12 as there are no real good vegetable sources. Unfortunately, by the time a deficiency does occur, it can cause irreversible nerve and brain damage.
In order to absorb vitamin B 12, a person needs the “intrinsic factor” in their stomach. This factor is made in the stomach, but if a person has part or all of their stomach removed, their ability to make intrinsic factor is reduced or eliminated. Basically, the intrinsic factor allows your body to absorb vitamin B 12 and without it, even if you eat foods rich in vitamin B 12, you can still develop a deficiency. In the case of someone having their stomach removed, vitamin B 12 can be administered by injection which must be continued every three weeks for the remainder of life. This method of vitamin administration ensures that it is delivered directly into the blood and bypasses the stomach where the intrinsic factor is insufficient or missing.
One exceptional food is calves liver (one pound per day) which is so high in vitamin B 12 that even people who lack the intrinsic factor absorbed enough vitamin B 12 to prevent pernicious anemia.