The blood that circulates throughout the body performs a number of critical functions. It delivers oxygen, removes carbon dioxide, and carries life-sustaining nutrients. By transporting long-distance messengers such as hormones, blood helps the various parts of the body communicate with each other. These important functions are performed by blood cells working in partnership with the liquid part of the blood (plasma). Most of the cells in it are red blood cells (erythrocytes). White blood cells (leukocytes) are also present in smaller numbers. Their role is to defend your body against foreign material, including infections, viruses, and fungi.
Anemia is a state that occurs when hemoglobin (an iron-protein compound in red blood cells that transports oxygen) is decreased and your body has too few red blood cells. When there are too few red blood cells due to a lack of vitamin B12, the condition is described as pernicious anemia. The term pernicious was adopted many years ago when there was no effective treatment and this condition was inevitably fatal. Today, excellent therapies are available and most people can lead a normal life with very little adverse effects.
Pernicious anemia can affect all racial groups, but the incidence is higher among fair-haired people, especially those whose ancestors came from Scandinavia or Northern Europe. It usually doesn't appear before the age of 30, although a juvenile form of the disease can occur in children. About 4% of Canadians have insufficient blood levels of vitamin B12.
Alternative names for pernicious anemia are vitamin B12 deficiency (malabsorption), Addison's anemia, and congenital pernicious anemia.