Folate

Folate is a water-soluble B vitamin (B9) essential for one-carbon transfer reactions that support DNA synthesis, repair, and methylation. It is necessary for cell division and growth and is especially important during pregnancy and infancy. Natural folates occur in foods as polyglutamates; synthetic folic acid is used in supplements and fortification and is more bioavailable.

Dietary sources include leafy green vegetables, legumes, citrus fruits, and fortified grains. Absorption occurs mainly in the upper small intestine after deconjugation of polyglutamates. Once absorbed, folates are reduced and methylated to form 5-methyltetrahydrofolate, the primary circulating form. In the body, folate provides one-carbon units for synthesis of purines and thymidylate, and for remethylation of homocysteine to methionine.

Recommendations commonly cited are 400 micrograms dietary folate equivalents (DFE) per day for adults; pregnant women are advised about 600 µg DFE, and lactating women about 500 µg DFE. The tolerable upper intake level for synthetic folic acid from supplements and fortified foods is 1,000 µg per day for adults.

Deficiency can cause megaloblastic anemia and glossitis; prolonged deficiency may impair fetal neural tube closure and increase the risk of neural tube defects. Risk factors include poor intake, malabsorption, alcohol use, and certain medications. Folate status is typically assessed by measuring serum and red blood cell folate, sometimes with homocysteine levels.

Safety considerations include the potential for high intakes of folic acid to mask vitamin B12 deficiency, which can lead to neurological complications if not addressed. Folate status is best supported by a balanced diet, with supplementation when indicated, such as for women planning pregnancy.