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Folate Deficiency

(Folic Acid)


Larry E. Johnson

, MD, PhD, University of Arkansas for Medical Sciences

Reviewed/Revised Nov 2022
Topic Resources

Folate deficiency is common. It may result from inadequate intake, malabsorption, or use of various drugs. Deficiency causes megaloblastic anemia (indistinguishable from that due to vitamin B12 deficiency). Maternal deficiency increases the risk of neural tube birth defects. Diagnosis requires laboratory testing to confirm. Measurement of neutrophil hypersegmentation is sensitive and readily available. Treatment with oral folate is usually successful.

Folate is now added to enriched grain foods in the US and Canada. Folate is also plentiful in various plant foods and meats, particularly raw green leafy vegetables, fruits, organ meats (eg, liver), but its bioavailability is greater when it is in supplements or enriched foods than when it occurs naturally in food (see table ).

Folates are involved in red blood cell maturation and synthesis of purines and pyrimidines. They are required for development of the fetal nervous system. Absorption occurs in the duodenum and upper jejunum. Enterohepatic circulation of folate occurs.

Folate supplements do not protect against coronary artery disease or stroke (even though they lower homocysteine levels); current evidence does not support claims that folate supplementation increases or reduces the risk of various cancers. Any role for using supplemental folate, methyltetrahydrofolate, or L-methylfolate, or for testing for mutations in the 5,10-methylenetetrahydrofolate reductase (MTHFR) gene in patients with depression is uncertain at this time.

Women taking both oral contraceptives and antiseizure drugs may need to take folate supplements to maintain birth control effectiveness.

Etiology of Folate Deficiency

The most common causes of folate deficiency are

Deficiency can also result from inadequate bioavailability and increased excretion (see table ).


Prolonged cooking destroys folate, predisposing to inadequate intake. Intake is sometimes barely adequate (eg, in people with alcohol use disorder). Liver stores provide only a several-month supply.

Alcohol interferes with folate absorption, metabolism, renal excretion, and enterohepatic reabsorption and reduces healthy food intake. 5-Fluorouracil, metformin, methotrexate, phenobarbital, phenytoin, triamterene, and trimethoprim impair folate metabolism.

In the US and Canada, many dietary staples (eg, cereals, grain products) are routinely enriched with folate, tending to reduce risk of deficiency.

Symptoms and Signs of Folate Deficiency

Folate deficiency may cause glossitis, diarrhea, depression, and confusion. Anemia may develop insidiously and, because of compensatory mechanisms, be more severe than symptoms suggest.

Diagnosis of Folate Deficiency

  • Complete blood count and serum vitamin B12 and folate levels

If serum folate is < 3 mcg/L or ng/mL (< 7 nmol/L), deficiency is likely. Serum folate reflects folate status unless intake has recently increased or decreased. If intake has changed, erythrocyte (red blood cell) folate level better reflects tissue stores. A level of < 140 mcg/L or ng/mL (< 305 nmol/L) indicates inadequate status.

Also, an increase in the homocysteine level suggests tissue folate deficiency (but the level is also affected by vitamin B12 and vitamin B6 levels, renal insufficiency, and genetic factors). A normal methylmalonic acid (MMA) level may differentiate folate deficiency from vitamin B12 deficiency, because MMA levels rise in vitamin B12 deficiency but not in folate deficiency.

Treatment of Folate Deficiency

  • Supplemental oral folate

Folate 400 to 1000 mcg orally once a day replenishes tissues and is usually successful even if deficiency has resulted from malabsorption. The normal requirement is 400 mcg/day. (CAUTION: In patients with megaloblastic anemia, vitamin B12 deficiency must be ruled out before treating with folate. If vitamin B12 deficiency is present, folate supplementation can alleviate the anemia but does not reverse, and may even worsen, neurologic deficits.)

For pregnant women, the recommended daily allowance (RDA) is 600 mcg/day. For women who have had a fetus or infant with a neural tube defect, the recommended dose is 4000 mcg/day, started 1 month before conception (if possible) and continued until 3 months after conception.

Key Points

  • Most commonly, folate deficiency results from reduced intake (eg, due to alcohol use disorder), increased demand (eg, due to pregnancy), or impaired absorption (eg, due to drugs or malabsorption disorders).

  • Prolonged cooking destroys folate, but many dietary staples are supplemented with folate.

  • Deficiency causes megaloblastic anemia and sometimes glossitis, diarrhea, depression, and confusion.

  • Measure serum folate and vitamin B12 levels in patients who have megaloblastic anemia.

  • To treat deficiency, give patients supplemental folate 400 to 1000 mcg orally once a day.

Drugs Mentioned In This Article

Drug Name Select Trade
Adrucil, Carac, Efudex, Fluoroplex, Tolak
Fortamet, Glucophage, Glucophage XR, Glumetza, Riomet, RIOMET ER
Otrexup, Rasuvo, RediTrex, Rheumatrex, Trexall, Xatmep
Luminal, Sezaby
Dilantin, Dilantin Infatabs, Dilantin-125, Phenytek
Primsol, Proloprim, TRIMPEX
NOTE: This is the Professional Version. CONSUMERS: View Consumer Version
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