Folate Deficiency: Anemia, Pregnancy Risks, and How Levels Are Checked

Short answer: Folate is a B vitamin the body cannot make in useful amounts on its own, so it must come from food or supplements. A shortfall can impair cell division and DNA synthesis, leading to anemia and, during early pregnancy, a meaningfully higher risk of neural tube defects in the developing baby.

What Folate Does in the Body

Folate, also called vitamin B9, works as a coenzyme in several core processes. According to the NIH Office of Dietary Supplements (ODS), its main physiological roles are:

• Acting as a coenzyme or cosubstrate in single-carbon transfers required for the synthesis of nucleic acids, meaning DNA and RNA.
• Supporting amino acid metabolism, including the conversion of homocysteine to methionine in the synthesis of S-adenosyl-methionine, an important methyl donor.
• Enabling the methylation of deoxyuridylate to thymidylate during DNA formation, a step that is required for proper cell division.

Because rapidly dividing cells depend heavily on DNA synthesis, tissues that turn over quickly, such as red blood cells and the cells lining the digestive tract, are among the first to show signs of a deficiency.

What Happens When Folate Is Low

Megaloblastic Anemia

When folate is insufficient, red blood cell precursors cannot divide normally. They grow abnormally large but immature, a condition called megaloblastic anemia. Symptoms can include fatigue, weakness, pale skin, shortness of breath, and difficulty concentrating. A clinician can distinguish folate-related megaloblastic anemia from the similar picture caused by vitamin B12 deficiency through blood testing, which matters because the treatments differ.

Neural Tube Defects in Pregnancy

The neural tube, the embryonic structure that becomes the brain and spinal cord, closes within the first 28 days after conception, often before a person knows they are pregnant. The NIH ODS rates the evidence as strong that adequate folic acid taken before conception and in early pregnancy helps prevent neural tube defects such as anencephaly and spina bifida. Because the critical window comes so early, public health guidance in many countries recommends that people who could become pregnant consume sufficient folic acid consistently, not just after a positive pregnancy test.

Elevated Homocysteine

Low folate status is associated with higher blood homocysteine levels. The NIH ODS notes moderate-strength evidence that folate supplementation, alone or combined with other B vitamins, reduces the risk of stroke, particularly in populations with low baseline folate status. This is thought to relate partly to homocysteine metabolism, though research is ongoing.

Daily Targets and Upper Limits

The NIH ODS expresses folate requirements in Dietary Folate Equivalents (DFE) because synthetic folic acid from supplements and fortified foods is absorbed more readily than the folate naturally present in whole foods. The adult Recommended Dietary Allowance is 400 mcg DFE per day. Pregnancy raises the target to 600 mcg DFE, and lactation to 500 mcg DFE.

Folate found naturally in foods and beverages is not considered harmful and has no established upper limit. For synthetic folic acid from supplements and fortified foods, the NIH ODS sets the Tolerable Upper Intake Level at 1,000 mcg per day for adults. Staying at or below that level is advised unless a health care provider recommends otherwise.

A key safety concern noted by the ODS is that high folic acid intake can mask a vitamin B12 deficiency. The anemia may appear to improve while nerve damage from B12 deficiency continues to progress, potentially becoming irreversible. This is one reason testing matters before starting high-dose supplementation.

Supplements are not intended to diagnose, treat, cure, or prevent any disease, and these statements have not been evaluated by the FDA.

How Folate Levels Are Checked

A clinician can assess folate status through blood tests. Serum folate reflects recent dietary intake, while red blood cell folate provides a longer-term picture of tissue stores, roughly over the past two to three months. Elevated homocysteine can also signal low folate or B12 status, though it is not specific to folate alone. If you have symptoms of anemia or belong to a higher-risk group, ask your doctor which tests are appropriate for your situation.

Who May Be at Higher Risk of Deficiency

• People with alcohol use disorder, since alcohol interferes with folate absorption and increases urinary excretion.
• People with malabsorptive conditions such as celiac disease or inflammatory bowel disease.
• Pregnant people or those planning pregnancy.
• People taking certain medications (see below).

Medication Interactions to Know

Talk to your doctor or pharmacist before combining folate supplements with any medication. The NIH ODS highlights three interactions in particular:

• Methotrexate (Rheumatrex, Trexall): When used to treat cancer, this drug works by inhibiting dihydrofolate reductase. Folate supplements can interfere with that mechanism. Patients should consult their provider before supplementing.
• Antiepileptic medications such as phenytoin (Dilantin), carbamazepine (Carbatrol, Tegretol, Equetro, Epitol), and valproate (Depacon): these can reduce blood folate levels, and folate supplements can in turn reduce blood levels of these medications, potentially affecting seizure control.
• Sulfasalazine (Azulfidine), used for ulcerative colitis: this drug inhibits intestinal folate absorption and can cause folate deficiency.

What the Evidence Does and Does Not Support

The NIH ODS grades the evidence on folate across several health areas. Here is a plain summary:

• Strong evidence: Folate is required for DNA and RNA synthesis, amino acid metabolism, and normal cell division. Adequate folic acid before and in early pregnancy helps prevent neural tube defects.
• Moderate evidence: Folate supplementation, alone or with other B vitamins, reduces stroke risk, especially in low-folate populations.
• Limited evidence: Folate naturally present in food may lower the risk of some cancers, while high-dose folic acid may have complex and possibly harmful effects. Folate supplements, particularly the form called 5-MTHF, may improve depression or antidepressant response in some people.
• Insufficient evidence: Folic acid supplementation improving cognitive function or preventing dementia or Alzheimer's disease. Periconceptional folic acid reducing the risk of autism spectrum disorder in offspring.

Grading evidence honestly means acknowledging that promising associations in early research do not always hold up in rigorous trials. Consult a clinician for guidance tailored to your health history.

A Note on Personal Dosing

The figures above are population reference values from the NIH ODS. They are not personal prescriptions. Your own needs may differ based on genetics, health conditions, medications, and diet. Please consult a clinician or pharmacist before starting or adjusting a folate supplement, and always discuss supplementation with your doctor if you take any prescription medication.

Sources: NIH Office of Dietary Supplements Folate Fact Sheet for Health Professionals and Consumer Fact Sheet, available at ods.od.nih.gov.