Slow-developing disease in which vitamin B 12 (see vitamin B complex ) deficiency impairs red-blood-cell production.
It can result from a diet lacking in vitamin B 12 or when intrinsic factor, a substance needed for intestinal absorption of B 12 , 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 B 12 injections into muscle soon reverses the anemia, but the injections must be continued for life.