Diseases & Conditions


Folate (Folic Acid)

Folate (folic acid), with vitamin B 12 , is necessary for the formation of normal red blood cells and the synthesis of DNA (deoxyribonucleic acid), which is the genetic material of cells. Folate is also necessary for normal development of a fetus's nervous system. A low intake of folate may increase the risk of bone fractures in older adults. Whether folate supplementation can improve cognitive function in older adults remains unclear.

In the United States, folate is added to enrich foods made from grains. Folate in supplements or in enriched foods is easier for the body to absorb than the folate that occurs naturally in food.

Folate Deficiency

Not eating enough raw leafy vegetables and citrus fruits can cause folate deficiency. Anemia can develop, causing fatigue, paleness, irritability, shortness of breath, and dizziness. A severe deficiency may result in a red and sore tongue, a reduced sense of taste, weight loss, depression, tingling or loss of sensation in the hands and feet, muscle weakness, loss of reflexes, difficulty walking, confusion, and dementia. The diagnosis is based on blood tests. Folate supplements taken by mouth usually correct the deficiency.

Because the body stores only a small amount of folate, a diet lacking in folate leads to a deficiency within a few months. Folate deficiency is common because many people do not eat enough raw leafy vegetables or citrus fruits. Also, prolonged cooking destroys much of the folate in food. Common causes of deficiency include undernutrition and alcoholism, particularly when combined. Alcohol consumed in large amounts interferes with the absorption and processing (metabolism) of folate. Malabsorption disorders interfere with absorption of folate. Certain anticonvulsants (such as phenytoin and phenobarbital) and drugs used to treat ulcerative colitis (such as sulfasalazine) decrease the absorption of this vitamin. Methotrexate (used to treat cancer and rheumatoid arthritis), triamterene (used to treat high blood pressure), metformin (used to treat diabetes), and trimethoprim-sulfamethoxazole (an antibiotic) interfere with the metabolism of folate.

Women who are pregnant or breastfeeding and people undergoing dialysis may develop this deficiency because their need for folate is increased.

Folate deficiency causes an anemia similar to that due to vitamin B 12 deficiency.


Anemia develops gradually and may be more severe than symptoms suggest. Fatigue may be the first symptom. In addition to the general symptoms of anemia (such as paleness, irritability, shortness of breath, and dizziness), folate deficiency, if severe, may result in a red and sore tongue, a reduced sense of taste, weight loss, and depression. If a pregnant woman has folate deficiency, her infant may have a birth defect of the spinal cord or brain (neural tube defect).

Did You Know...

Cooking can destroy most of the folate in foods. If a pregnant woman has folate deficiency, her fetus may have a birth defect of the brain or spinal cord.


If a blood test detects large red blood cells in people who have anemia or who are undernourished, doctors measure the folate level in a blood sample. A low level indicates this deficiency. Doctors also measure the vitamin B 12 level to rule out vitamin B 12 deficiency because this deficiency can also result in anemia and large red blood cells.

Prevention and Treatment

As a preventive measure, people who are taking drugs that interfere with the absorption or metabolism of folate should take a folate supplement. Women who are pregnant or who could become pregnant should take folate supplements to reduce the risk of having an infant with a birth defect. Women who have had a baby with a neural tube defect are often prescribed higher doses of folate. Folate supplementation has not been proven to reduce cardiovascular disease but may reduce strokes.

Treatment consists of taking daily doses of a folate supplement by mouth.

Folate Excess

Folate is generally not toxic. If people with vitamin B 12 deficiency take very high doses of folate, doctors may be delayed in recognizing the nerve damage due to vitamin B 12 deficiency. Because the diagnosis is delayed, nerve damage may be more severe and more difficult to treat.

Last full review/revision August 2007 by Larry E. Johnson, MD, PhD

Source: The Merck Manual Home Edition