Vitamin B12 (cyanocobalamin) is necessary for the normal use of folic acid (another B vitamin), which is needed for the normal formation of RBCs. A deficiency of either will result in very large RBCs, which are destroyed when moving through the tiny capillaries, which results in anemia. Vitamin B12 absorption depends upon adequate amounts of intrinsic factor, released within the stomach. Low levels of intrinsic factor is the main cause of Vitamin B12 deficiency, but deficiency may also be caused by lack of stomach acid or decreased absorption within the small intestines. Blood levels reflect recent dietary intake; more accurate levels indicating deficiency are obtained through MMA (urinary methymalonic acid) testing. MMA/creatinine ratio is very specific for the level of deficiency within cells and tissues. Low levels are seen during normal pregnancy, in conjunction with folic acid or vitamin C deficiency, following resection of the small intestine, stomach surgery, IBS (irritable bowel syndrome), pernicious anemia, atrophic gastritis, or intestinal parasites. High levels are seen in people with liver disease, polycythemia vera, or leukemia.
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