Folate is a water-soluble B vitamin (vitamin B9) your body needs for DNA building, cell division, and red blood cell production, but cannot make on its own. You get folate from foods like leafy greens, legumes, and fortified grains, or from supplements. Folic acid is the synthetic form used in supplements and food fortification, and your body converts it into active folate.

Folate is essential for building and repairing DNA - the genetic blueprint inside every cell. Because it powers cell division, folate is especially important during rapid growth and repair, including pregnancy, infancy, and tissue healing. When folate is adequate, cells can replicate accurately and tissues can renew normally. When folate is low, cell division slows and body systems with fast turnover (like bone marrow) are affected first.

Low folate can cause fatigue, weakness, pallor, shortness of breath, and “brain fog” due to impaired oxygen delivery from abnormal red blood cells. It may also be linked to mood changes, memory problems, and tingling in the hands and feet. Because folate supports neurotransmitter production and blood formation, deficiency can present as cognitive and mood symptoms alongside anemia-related complaints.

Folate is required for proper DNA synthesis in developing red blood cells. When folate is insufficient, red blood cell precursors can’t divide normally, so they become large, immature cells (megaloblasts). This leads to macrocytic (megaloblastic) anemia, where red blood cells are oversized and less efficient at carrying oxygen. The result is fatigue, poor exercise tolerance, and other anemia symptoms tied to reduced oxygen delivery.

Folate needs rise substantially in pregnancy, and adequate folate before conception and in early pregnancy helps protect fetal brain and spinal cord development. Low maternal folate is strongly associated with increased risk of neural tube defects. Folate testing can flag low levels early - before pregnancy or in the first trimester - so supplementation and dietary changes can be started promptly to support healthy fetal development.

Low folate usually suggests inadequate intake, poor absorption, increased demand (such as pregnancy), or interference from alcohol or certain medications, and it can lead to macrocytic anemia and neurological symptoms. Optimal folate supports normal DNA synthesis, methylation, and red blood cell maturation - often reflected by mid-to-upper reference range values. High folate is most often from supplements or fortified foods and can sometimes mask vitamin B12 deficiency.

Folate and vitamin B12 work together to form healthy red blood cells and support nervous system function. A CBC helps detect anemia patterns (like macrocytosis), while vitamin B12 testing helps distinguish folate deficiency from B12 deficiency for targeted treatment. This matters because high folate intake can partially correct anemia while B12-related neurological damage continues. Interpreting folate alongside B12 and CBC gives a clearer clinical picture.

Low folate can be caused by low dietary intake (not enough leafy greens, legumes, or fortified grains), chronic alcohol use, and malabsorption disorders such as celiac disease. Increased demand (notably pregnancy) can also outpace intake. Certain medications can interfere with folate metabolism or absorption, including anticonvulsants and methotrexate. These factors can reduce folate availability and contribute to anemia, fatigue, and neurological symptoms.

High folate levels are rarely caused by disease and most often reflect supplementation or high intake of fortified foods. While excess folate is generally excreted, elevated folate can mask vitamin B12 deficiency by improving the anemia pattern without fixing the underlying B12 problem. This can delay diagnosis while neurological damage progresses. In rare situations, very high levels may be linked to unmetabolized folic acid circulating in the blood.

Serum folate reflects recent folate intake and short-term status, so it can change with diet or supplements. Red blood cell (RBC) folate is considered a better indicator of longer-term tissue stores because it reflects folate levels during red blood cell formation over time. Depending on the clinical question - recent intake versus longer-term status - your clinician may use one or both tests, often alongside vitamin B12 and a CBC.