Slow-developing disease in which vitamin B12 (see vitamin B complex) deficiency impairs red-blood-cell production. It can result from a diet lacking in vitamin B12 or when intrinsic factor, a substance needed for intestinal absorption of B12, either is not produced by stomach cells or cannot bind to the vitamin. It causes weakness, waxy pallor, shiny tongue, and stomach, intestinal, and neurological problems. Its slow development can allow anemia to become very severe by the time of diagnosis. Monthly B12 injections into muscle soon reverses the anemia, but the injections must be continued for life.
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