Causes
B12 and folate deficiency may be due to insufficient intake, inadequate absorption, increased loss, or to increased need. Folate (also called folic acid) is found in leafy green vegetables, citrus fruits, dry beans, yeast, and fortified cereals. B12 is found in animal proteins such as red meat, fish, poultry, milk, eggs, and in fortified cereals. Deficiency due to insufficient intake of B12 is uncommon but may be seen in vegetarians and their children who do not consume any animal products.
B12 deficiencies also can be caused by insufficient stomach acid necessary to separate B12 from ingested protein (the most common cause in the elderly) or a lack of intrinsic factor, a substance produced by parietal cells in the stomach that binds with B12 before absorption by the intestines. An autoimmune condition called pernicious anemia involves damage to these parietal cells, resulting in decreased production of intrinsic factor.
Both B12 and folate deficiencies can also arise with diseases or conditions that cause general malabsorption, such as: celiac disease (an intolerance to wheat that causes inflammation and malabsorption), bacterial overgrowth in the stomach and intestines, or surgery that removes part of the stomach (and the parietal cells) or the intestines.
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