Folate Deficiency

Epidemiology

• Folate deficiency is rare in the US since mandated folic acid fortification of grain products in 1998.
• The prevalence of folate deficiency anemia in a study of US community dwelling adults was found to be <0.1%.
  • Odewole OA, Williamson RS, Zakai NA, et al. Near-elimination of folate-deficiency anemia by mandatory folic acid fortification in older US adults: Reasons for Geographic and Racial Differences in Stroke study 2003-2007. Am J Clin Nutr. 2013;98(4):1042-1047. doi:10.3945/ajcn.113.05968.
• In developing countries, folate deficiency contributes more substantially to the overall anemia burden.

Risk Factors for Folate Deficiency

• Individuals with inadequate dietary intake (elderly, alcohol use disorder)
• Malabsorption disorders
• Pregnant and lactating women due to increased demands
• Infants exclusively fed goat’s milk.

Pathophysiology

• Unlike the complicated absorption of B12, folate does not have as many steps to its process. Folate polyglutamates are cleaved to monoglutamates and absorbed in the lumen of the jejunum.
• In order to be utilized, folate is reduced to dihydrofolate and then to tetrahydrofolate (THF) by a series of enzymatic steps, in which B12 is necessary.
• Folate is essential for DNA synthesis through its role in methylation of compounds to eventually create both the purines and pyrimidines needed for DNA.
• Deficiency impairs DNA synthesis, leading to megaloblastic changes characterized by cells with large, malformed nuclei.
• Given hematopoietic precursor cells are among the most rapidly dividing cells in the body, they are very sensitive to this abnormal DNA synthesis. This leads to ineffective erythropoiesis, intramedullary death of erythrocytes, and reduced red cell life span.

Homocysteine and Methylmalonic Acid Pathways and Their Relationship with Folate

• Folate deficiency (tetrahydrofolate or THF in the graph above) is required for homocysteine to become methionine. Therefore, folate deficiency can cause an elevation of homocysteine levels in blood (can be used as an adjunct testing in folate deficiency and vitamin B12 deficiency).
• Importantly, elevation of methylmalonic acid or MMA occurs only in B12 deficiency and it helps to differentiate folate vs vitamin B12 deficiency.

Causes of Folate Deficiency

• Dietary insufficiency: Elderly individuals, alcohol use disorder, strict vegan/vegetarian diets, anorexia or those with reduced oral intake from chronic diseases.
• Malabsorption: Celiac disease, inflammatory bowel disease (e.g. Crohn’s disease), surgery (e.g. gastric bypass).
• Increased demand: Pregnancy, lactation, hemolysis, exfoliative skin diseases, dialysis.
• Medications: Anticonvulsants, folate antagonists (methotrexate, trimethoprim, pyrimethamine).
• Social determinants: Birth outside the US, homelessness, alcohol use disorder.
• Others: smoking, and other recreational drug use.

Dietary Sources of Folate

Think of “foliage” which may help you remember that folate is mostly found in vegetable sources (not exclusively). Dietary sources of folic acid include:

• Vegetables (especially dark green leafy vegetables).
• Fruits and fruit juices.
• Nuts.
• Peas.
• Beans.
• Seafood.
• Eggs.
• Dairy products.
• Meat and poultry.
• Grains.
• Spinach.
• Liver.
• Asparagus and brussels sprouts.

In January 1998, the U.S. Food and Drug Administration (FDA) began requiring manufacturers to add 140 mcg folic acid/100 g to enriched breads, cereals, flours, corn meals, pastas, rice, and other grain products. The fortification program increased mean folic acid intakes in the United States by about 190 mcg/day.

Clinical Manifestations of Folate Deficiency

• Megaloblastic macrocytic anemia.
  • Nonspecific symptoms of anemia (fatigue, irritability, pallor, headaches, etc.)
• Oral ulcers, sore tongue, angular cheilosis (cells of the oral mucosa divide rapidly and are thus sensitive to the lack of nucleic acids that occurs when folate is deficient).
• Cognitive slowing and neuropathy (although much more commonly associated with B12 deficiency).
• Depression (twice as common in folate deficiency than in B12 deficiency).
• Neural tube defects during embryonic development.
• Hyperhomocystenemia, rarely leading to thrombotic events.

Differentiating Between Folate and Vitamin B12 Deficiency

Similarities:

• Nearly identical megaloblastic macrocytic anemia, cytopenias, hypersegmented neutrophils.
• Clinical manifestations of anemia can be quite similar.
  • Both can exhibit the nonspecific anemia symptoms mentioned above.
  • Both can exhibit the oral/gastrointestinal symptoms mentioned above.
  • Both can cause nerve damage to a different degree.
• Laboratory findings: Homocysteine is elevated in both deficiencies.

Differences:

• Clinical manifestations: Vitamin B12 deficiency causes neurologic symptoms including paresthesias, loss of vibration sense, ataxia, impaired gait, cognitive impairment, depression, psychosis.
  • In severe cases, subacute combined degeneration of the spinal cord can occur due to progressive demyelination.
  • Folate deficiency alone will not cause the extent of neurologic symptoms seen with B12 deficiency.
• Laboratory findings: Methylmalonic acid (MMA) is elevated specifically in B12 deficiency, and will not be elevated in isolated folate deficiency.
• Body stores:
  • Total body stores of folate are approximately 0.5 to 20 mg, while B12 stores are in the range of 2 to 5 mg.
  • Deficiency of folate can develop within weeks to months, or more rapidly if demands are increased, while B12 deficiency typically does not develop for at least one to two years, sometimes longer.

Coexistence of B12 and Folate Deficiency

• Occurs in approximately 10% of patients with either deficiency.
• If this occurs, clinical manifestations are mainly those of B12 deficiency.
• Never administer folic acid supplementation alone if suspecting coexistence, as this may precipitate or worsen neurologic complications.

Diagnosis of Folate Deficiency

Folate deficiency anemia is diagnosed through a combination of clinical presentation, peripheral blood findings, and specific laboratory measurements of folate status.

Serum Folate

• Deficiency: <4 ng/mL (or <6.8 nmol/L) indicates negative folate balance.
• Normal range: 6-20 ng/mL.
• Serum folate <6 μg/L (or 14 nmol/L) shows significant effects on red cell indices
• Depletion threshold: <8 μg/L (or 18 nmol/L) correlates with rising homocysteine and should be considered the decision limit
• Note that serum folate reflects recent dietary intake and can drop before tissue depletion occurs, requiring repeated measurements for definitive diagnosis

Red Blood Cell (RBC) Folate

• Deficiency: <140 ng/mL (or <400 nmol/L).
• RBC folate is the best test for long-term folate deficiency and correlates well with tissue stores.
• Reflects folate status over the preceding ~4 months in healthy individuals (shorter in CKD due to reduced RBC lifespan)

Homocysteine

• Elevated: >14 μmol/L (though different laboratories use different upper limits)
• Affected by vitamin B6 status, age, gender, and renal insufficiency

Complete Blood Count (CBC)

• Macrocytic anemia with MCV >110 fL in most cases (though may be lower with coexisting iron deficiency, thalassemia trait, or inflammatory disease).
• Leukopenia and thrombocytopenia may be present.

Peripheral Blood Smear

• Hypersegmented neutrophils (key finding) : There are two main criteria for hypersegmentation. First, having at least one neutrophil with 6 or more lobes in the nucleus. Second, 5% or more of neutrophils have 5 or more lobes.
• Oval macrocytosis.
• Basophilic stippling.
• Howell-Jolly bodies.
• Occasional circulating megaloblasts.

Other Laboratory Findings

• Elevated lactate dehydrogenase due to ineffective erythropoiesis.
• Increased bone marrow storage iron and serum ferritin in most cases.

Combined assessment using markers of both abundance (serum/RBC folate) and cellular use (homocysteine) provides the most comprehensive evaluation. In cases of discordance between laboratory results and strong clinical features, treatment should not be delayed.

Management of Folate Deficiency

• The standard treatment for folate deficiency anemia is oral folic acid supplementation.
• Unlike B12 deficiency, rapid correction of folate is not usually required, given the dangerous neurologic effects predominate with B12 deficiency, and not folate.
• Times where rapid correction could be warranted include pregnancy (where the developing fetus could be affected), or in neonates and infants (whose development may be impacted)
• Dosing:
  • Oral folate 1 to 5 mg daily for one to four months or until there is laboratory evidence of hematologic recovery.
  • 1 mg daily is usually enough given the recommended dietary allowance is 0.2 mg.
  • Intravenous or subcutaneous folic acid (0.4 to 1 mg daily) may be necessary for the rapid correction of severe or symptomatic anemia caused by folate deficiency, or in pregnant, infant, or neonatal patients as mentioned above.
  • It is also suitable for individuals unable to tolerate oral medication, such as those with vomiting or obtundation.
  • If the folate deficiency is due to a persistent issue, such as chronic hemolytic anemia, treatment may need to be continued indefinitely, usually orally 1 mg daily.
  • If not due to a persistent/nonreversible cause, and adequate dietary intake is achieved, supplementation could be stopped while adequately monitoring for the anemia afterward.
• Monitoring response:
  • The initial response to folate supplementation mirrors the response observed when supplementing for B12 deficiency:
    • Reticulocytosis within 3-5 days.
    • Initial increased hemoglobin levels over 1-2 weeks with normalization in 4-8 weeks.
    • Other cytopenias resolving somewhere between 2-4 weeks.
    • Hypersegmented neutrophils should resolve between day 10-14
  • Assaying serum folate levels to confirm correction is an option, though often unnecessary if expected improvements in hematologic and clinical manifestations occur.
  • If not severe, consider repeat CBC 8-12 weeks after supplementation starts.
  • In severe cases (e.g., pregnant individuals, infants, or neonates), repeat testing of CBC, folate levels, and homocysteine should be considered after four weeks, and therapy should be adjusted accordingly.