Vitamin B-12, also called cobalamin, is needed to make DNA, nerve tissue and red blood cells. Lack of vitamin B-12 or its absorption eventually causes abnormal red blood cell development. The spleen functions to filter the blood and remove dead and abnormal red and white blood cells out of circulation. Too many abnormal blood cells clog the filtering tissues of the spleen, leading to enlargement and tenderness.
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Vitamin B-12 Function
Vitamin B-12 is required for the timely synthesis of DNA during cell division, to produce myelin, the protective sheath surrounding nerves that allows for efficient flow of electrical signals, and for the proper development of red blood cells in bone marrow. The timely construction of DNA helixes is especially important in tissues where cells are dividing rapidly, such as the bone marrow, where red blood cells are formed before being released into the bloodstream. The recommended daily allowance for vitamin B-12 ranges from 0.4 micrograms in infants under six months old to 2.8 micrograms for lactating females, according to the Office of Dietary Supplements. Adult males require 2.4 micrograms daily.
Vitamin B-12 Deficiency
Chronic lack of vitamin B12 results in deficiency symptoms. Vegetarians who avoid meat, poultry, fish and dairy products are at higher risks for developing vitamin B-12 deficiency. Symptoms of deficiency include peripheral neuropathy, such as tingling, numbness and weakness in the limbs, reduced brain function, such as memory loss and cognitive deficits, and macrocytic anemia. Macrocytic, or megaloblastic, anemia is characterized by the presence of abnormally large and structured red blood cells, or megaloblasts, that are immature in their development. Macrocytic anemia is usually caused by a deficiency or defective absorption of either vitamin B-12 or folic acid.
Deficiency and Spleen Enlargement
In addition to abnormal red blood cells, macrocytic anemia may also involve abnormal, immature white blood cells, called leukocytes, and blood platelets, called thrombocytes. The primary role of the spleen is to filter dead or abnormal cells from the bloodstream, but if too many cells need to be removed, then the filtering tissues of the spleen become clogged and ineffective. The large size of the abnormal blood cells also compounds the problem. The end result is a swollen and enlarged spleen unable to function properly. An enlarged spleen often becomes tender, which can be felt underneath the heart.
Vitamin B-12 Sources
Good sources of vitamin B-12 include most animal products, such as meat, poultry, fish, eggs, milk and butter. Vitamin B-12 also occurs in some plants, such as seaweeds and spinach, as well as many nuts and legumes. Fermented soy products contain vitamin B-12 also, but very little of it is able to be processed in the human gastrointestinal system. To normally absorb vitamin B-12 from food, a gastric protein known as intrinsic factor is required, which some people do not have due to genetic diseases.