Folate is a general term that applies to natural folates in food, and folic acid, the synthetic form used in supplements and fortified food (also called folacin). Folate is a coenzyme that is critical in the metabolism of DNA and RNA precursors and several amino acids, methylation reactions, and synthesis of red and white blood cells. An important interrelationship occurs between folate and vitamins B6 and B12 as all three function to regenerate methionine from homocysteine and prevent a build-up of blood homocysteine levels.
Folate deficiency results in impaired synthesis of DNA and RNA, thus reducing cell division. This is most apparent in rapidly multiplying cells such as red blood cells, epithelial cells of the digestive tract, and those involved in embryo development. An adequate intake of folate reduces the risk of neural tube defects such as spina bifida. As intake is often low, the folic acid is added to cereal foods sold in the USA and Canada. This has been credited with greatly reducing the incidence of infants with neural tube defects. Women who are pregnant or who may become pregnant are often advised to boost their folate status with a dietary supplement.
Folate deficiency can also cause macrocytic anemia and symptoms such as fatigue, diarrhea, irritability, forgetfulness, lack of appetite, and headache. Folate deficiency can result from dietary insufficiency, heavy alcohol consumption, conditions such as cancer that increase rates of cell division, malabsorption (e.g., inflammatory bowel diseases and celiac disease) , the use of several medications, and genetic diseases affecting its absorption or metabolism. Because high levels of blood folate can mask a true vitamin B12 deficiency, total folate intake should not exceed 1 mg daily . Concerns regarding the safety of excess folate intake are limited to the intake of synthetic folic acid.