B12 and folate deficiency may be due to insufficient intake, inadequate absorption, increased loss, or to increased need. Folate is found in leafy green vegetables, citrus fruits, dry beans, yeast, and fortified cereals. Folic acid is the synthetic form of folate that is used in medications and supplements. 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 vegans (who do not consume any animal products) and their breast-fed infants.
B12 deficiency can be caused by insufficient stomach acid, which is necessary to separate B12 from dietary protein. This is the most common cause of B12 deficiency in the elderly and in people taking medication that suppresses gastric acid production. Deficiency may also be due to a lack of intrinsic factor, a substance produced by special cells in the stomach called parietal cells. Intrinsic factor binds to B12 to enable absorption by the intestines. Without it, very little B12 can be absorbed. 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 of the gut that cause general malabsorption. These include coeliac disease (an intolerance to gluten that causes inflammation and malabsorption), bacterial overgrowth in the stomach and intestines, or surgery that removes part of the stomach, the parietal cells, or the intestines (including some forms of surgery used for treating obesity).
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), trimethoprim (an antibiotic sometimes given long-term) or methotrexate (an arthritis treatment).
All pregnant women need increased amounts of folate for proper development of the baby. Mothers with a low folate intake before pregnancy, or in the early weeks, are at increased risk of having a baby with a neural tube birth defect (spina bifida or anencephaly).