whw-class about vitamin B 12

Vitamin B12 (Cobalamin)

Vitamin B12 is unique in that it is the first cobalt-containing substance found to be an essential nutrient. It is the only vitamin that contains essential mineral elements. Animal protein is almost the only place that contains B12, although vegetarians can get it from microbial synthesis and from legume nodules where it is synthesized by microbes.

Vitamin B12 is necessary for normal metabolism of nerve tissue and is involved in protein, fat and carbohydrate metabolism. B12 aids folic acid in the synthesis of choline. It helps the placement of vitamin A into body tissues.

B12 is poorly absorbed unless intrinsic factor, a mucoprotein secreted in the stomach, is present. Autoimmune reactions in the body can bind intrinsic factor or can affect the cells that produce it. Absorption of B12 appears to decrease with age, and with iron, calcium and B6 deficiencies. Absorption increases during pregnancy.

Pernicious anemia develops insidiously and progressively as the large hepatic stores of B12 are depleted. It may take five or six years to develop. Usually the problem is more profound than what would be expected from the symptoms. This is due to physiologic adaptation. Splenomegaly and hepatomegaly may occasionally be seen. GI problems may be present, including anorexia, intermittent constipation and diarrhea and poorly localized abdominal pain. Considerable weight loss is common. Peripherial nerves are commonly involved, even in the absence of anemia. Second to this is spinal cord involvement beginning in the dorsal column with loss of vibratory sensation in the lower extremities, loss of position sense and ataxia. Lateral column involvement follows with spasticity and hyperactive reflexes and a Babinski’s sign. Some patients have irritability, mild depression or actual paranoia. Occasionally yellow-blue color blindness occurs.

Rare signs are fever of unknown origin that responds promptly to B12 therapy. Endocrine deficiencies, especially of the thyroid and adrenal glands, if they are associated with pernicious anemia, suggest an autoimmune basis for gastric mucosal atrophy. Hypogammaglobulinemia may be present.

Anemia is macrocytic with an MCV>100. There is a test for B12 levels. The schilling test measures the absorption of radioactive B12 with and without intrinsic factor.

J Allergy 2:183-5, 1951    B12 supplementation of 1000mcg IM once weekly for four weeks yielded the following results: 18/20 patients with intractable asthma improved. 9/10 patients with chronic urticaria improved. 6/6 patients with chronic contact dermatitis improved. Patients with atopic dermatitis–1/10 greatly improved, 5/10 moderately improved.

Folic acid and B12 are well known to be associated with megaloblastic anemia. Sickle cell patients have been found to respond to folic acid, which has been shown to reverse exacerbations of the disease (Am J Hematol 1987).

Riboflavin deficiency can lead to a normocytic, normochromic anemia that responds to supplementation. Thiamin deficiency can lead to a megaloblastic anemia. B6 deficiency may lead to a microcytic anemia.

Crohn’s Disease: May impair absorption of  all B vitamins. (Scand J Gastroenterol 14:1019-24 1979) Folic acid deficiency found in patients. Lancet: 1:849 1946–folic acid supplementation may decrease diarrhea.