Folic acid

Folic acid is the fully oxidized form of folate commonly used in fortified foods and dietary supplements. Folate, also known as vitamin B9, is a water-soluble vitamin that includes folic acid as well as naturally occurring reduced forms found in foods and tissues. Folic acid is a monoglutamate form, whereas naturally occurring food folates are typically reduced folate derivatives .¹

Folic acid is not itself the main biologically active form of folate. After absorption, it is converted through enzymatic reactions into reduced folate forms, including tetrahydrofolate and its derivatives. These compounds participate in one-carbon metabolism, a network of reactions that transfers small carbon-containing units between molecules .^1,2

Through these folate-dependent reactions, folate contributes to the synthesis of DNA and RNA building blocks and to the metabolism of several amino acids. Folate metabolism is also involved in converting homocysteine to methionine, supporting the production of S-adenosylmethionine, an important donor of methyl groups in cellular reactions .^1,2

Folic acid and folate are therefore related but not interchangeable terms. Folate refers to the broader family of vitamin B9 compounds, whereas folic acid refers to one specific oxidized form. Naturally occurring food folates are typically reduced tetrahydrofolate derivatives, often with several glutamate units attached .¹