B9vitamin

B9 vitamin, commonly called folate in natural dietary forms and folic acid in supplements, is a water-soluble B vitamin essential for one-carbon metabolism. It supports DNA synthesis and repair, RNA production, and the maturation of red blood cells.

In the body folates exist as tetrahydrofolate cofactors that transfer one-carbon groups for nucleotide and amino acid metabolism. Natural folates occur in foods, while synthetic folic acid is used in fortified foods and most supplements. Absorption occurs mainly in the duodenum and upper jejunum; folic acid is more bioavailable than natural folates.

Common dietary sources include leafy greens, legumes, citrus fruits, eggs, and fortified cereals. Intakes are expressed as dietary folate equivalents (DFE) to reflect differences in bioavailability.

Functions include synthesis of thymidylate and purines, methylation reactions, and amino acid metabolism. Adequate folate supports rapidly dividing tissues and fetal neural tube development during early pregnancy.

Deficiency can cause megaloblastic anemia and, in pregnancy, neural tube defects in the fetus. Symptoms include fatigue and glossitis. At-risk groups include pregnant people, those with malabsorption, heavy alcohol use, the elderly, and users of certain medications such as methotrexate or anticonvulsants.

Safety: excessive synthetic folic acid can mask B12 deficiency. The upper intake level for folic acid from fortified foods and supplements is 1000 mcg/day for adults; there is no UL for natural dietary folates. General guidelines recommend about 400 mcg DFE daily for adults, higher during pregnancy (about 600 mcg DFE).

In practice, supplement use is individualized; women who may become pregnant are often advised to take folic acid before conception and through early pregnancy.