There are a variety of causes of B12 and/or folate deficiencies. They include:
Insufficient dietary intake
B12 is found in animal products such as red meat, fish, poultry, milk, and eggs. Folate (also called folic acid) is found in leafy green vegetables, citrus fruits, dry beans, yeast, and fortified cereals. The human body stores several years' worth of B12 in the liver. Since it is readily available in the food supply, a dietary deficiency of this vitamin is extremely rare in the U.S. It may be seen sometimes with general malnutrition, in vegans (those who do not consume any animal products, including milk and eggs), and breastfed infants of vegans. Deficiencies in children and infants show up fairly quickly since they do not have the stores seen in adults.
Folate deficiency used to be a common, but in 1997 the US government mandated supplementation of cereals, breads, and other grain products with folic acid. Since this implementation, the number of women of child-bearing age with decreased folate levels was reduced from 21% to less than 1%. Because folate is stored in tissue in smaller quantities than B12, folate must be consumed more regularly than B12.
Both B12 and folate deficiencies may be seen with conditions that interfere with absorption in the small intestine. These may include:
- Celiac disease
- Bacterial overgrowth or the presence of parasites in the intestines
- Reduced stomach acid production; stomach acid is necessary to separate B12 from the protein in food. This is the most common cause of B12 deficiency in the elderly and in individuals on drugs that suppress gastric acid production.
- Pernicious anemia, the most common cause of B12 deficiency. Intrinsic factor (IF) is a protein made by parietal cells that line the stomach. B12 binds to intrinsic factor, forming a complex that is absorbed in the intestines. With pernicious anemia, little or no intrinsic factor is produced, thus preventing the absorption of B12.
- Surgery that removes part of the stomach (and the parietal cells) or the intestines may greatly decrease absorption, a concern that is considered when gastric by-pass procedures are performed.
- Chronic pancreatitis
All pregnant women need increased amounts of folate for proper fetal development. If a woman has a folate deficiency prior to pregnancy, it will be intensified during gestation and may lead to premature birth and neural tube defects in the child. People with cancer that has spread (metastasized) or with a chronic hemolytic anemia such as sickle cell have an increased need for folate.
- Chronic alcoholism can cause B12 and/or folate deficiency due to poor intake and impaired release of B12 from dietary proteins.
- Some drugs can cause B12 deficiency, for example, metformin and omeprazole, which cause B12 malabsorption and impaired release of B12 from food proteins due to decrease in gastric acids, respectively.
- Anti-seizure medications such as phenytoin can decrease folate as can drugs such as methotrexate, which blocks folate absorption and affect body metabolism and utilization of folate, respectively.