Until 1934, this form of anemia was invariably fatal. People survived for months or even years while growing ever weaker, but they eventually succumbed. Vitamin B 12 is needed throughout the body to make DNA, a cell's genetic material. So a shortage leads to impaired cell production. Often they never make it out of the bone marrow, where they're made.
Fatigue is only one of several possible symptoms of pernicious anemia.
Others include a burning tongue, tingling and numbness in the hands and feet, loss of appetite, irritability, mild depression, memory loss and vague stomach pains. Today doctors know that usually it is not a shortage of this nutrient in the diet but an inability of the body to absorb vitamin B 12 that causes deficiency problems. As people get older, they may have reduced production in their stomachs of an enzyme called intrinsic factor. Intrinsic factor escorts any vitamin B 12 that you've eaten across your intestinal lining into your bloodstream. As levels of intrinsic factor drop, less B 12 gets absorbed, and what's stored in the body gets used up.