Tetrahydrofolic acid is a folic acid derivative. It is produced from dihydrofolic acid by dihydrofolate reductase. It is converted into 5,10-methylenetetrahydrofolate by serine hydroxymethyltransferase. It is a coenzyme in many reactions, especially in the metabolism of amino acids and nucleic acids. It acts as a donor of a group with one carbon atom. It gets this carbon atom by sequestering formaldehyde produced in other processes. Tetrahydrofolate is the main active metabolite of dietary folate. It is vital as a coenzyme in reactions involving transfers of single carbon groups. Tetrahydrofolate has a role in nucleic and amino acid synthesis. As nucleic and amino acid synthesis is affected by a deficiency of tetrahydrofolate, actively dividing and growing cells tend to be the first affected. Tetrahydrofolate is used to treat topical sprue and megaloblastic and macrocytic anemias, hematologic complications resulting from a deficiency in folic acid. Tetrahydrofolic acid is used for nutritional supplementation, also for treating dietary shortage or imbalance.