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 complete vegetarians (who do not consume any animal products) and their breast-fed infants.
B12 deficiency can be caused by insufficient stomach acid - necessary to separate B12 from ingested protein. This is the most common cause of B12 deficiency in the elderly and individuals on drugs that suppress gastric acid production. Deficiency may also be due to a lack of intrinsic factor, a substance produced by parietal cells in the stomach that binds to B12 to enable absorption by the intestines. An autoimmune condition called pernicious anaemia involves damage to the 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: coeliac disease - an intolerance to gluten – found in edible grasses such as wheat, barley, rye and oats - 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.
chronic disorders such as liver or kidney disease, and alcoholism can lead to decreased levels of B12 or folate, as can medications such as phenytoin, metformin (diabetic therapy), or methotrexate (an arthritis treatment).
All pregnant women need increased amounts of folate for proper fetal development. Any deficiencies that are present prior to pregnancy will intensify during gestation. Folate deficiency in pregnancy has been associated with neural tube defects (spina bifida).