Folsyra

Folsyra, known in English as folic acid, is a water-soluble B vitamin (B9). It exists as natural folates in foods and as the synthetic form folic acid used in supplements and fortified foods. In the body, folic acid is reduced to dihydrofolate and then to tetrahydrofolate, the active coenzyme forms involved in one-carbon metabolism.

Natural folates are found in leafy greens, legumes, citrus fruits and some animal products; folic acid is widely added to cereals and other fortified foods. The synthetic form typically has higher bioavailability than natural folates, so dietary intake is often expressed as dietary folate equivalents.

Folate coenzymes participate in DNA synthesis, repair and methylation, and are essential for rapidly dividing cells. Deficiency can cause megaloblastic anemia and elevated homocysteine; in pregnancy, inadequate folate status increases the risk of neural tube defects in the fetus. Recommended intake for healthy adults is about 400 micrograms daily; pregnant individuals are advised to 600 micrograms, lactating individuals about 500 micrograms.

Folate deficiency is more common in populations with poor diets, alcoholism, certain malabsorption disorders, or increased needs. Excess intake from supplements or fortified foods can mask vitamin B12 deficiency and, at very high levels, has raised safety concerns; a tolerable upper intake level of 1000 micrograms per day is commonly advised for adults from supplements and fortified foods. Some medications interact with folate metabolism or absorption.

Folate status is improved by food fortification programs, and folic acid supplementation is routinely recommended for women planning pregnancy or who are pregnant. In Swedish terminology, folsyra refers to folic acid.