Folate (Vitamin B9) Deficiency: Symptoms, Tests, Intake, Foods

Vitamin B9 (folate) supports DNA synthesis, red blood cell formation, and several methylation reactions. Prolonged deficiency leads to megaloblastic anemia and, in pregnant women, increases the risk of neural tube defects if peri-conceptional intakes are insufficient. Recommended intake and safety guidelines are detailed in the NIH ODS professional fact sheet and the EFSA DRV synthesis.

Symptoms (mild deficit → megaloblastic anemia)

Fatigue, weakness, pallor, shortness of breath on exertion
Glossitis (smooth/red painful tongue), stomatitis
Discrete neuro-cognitive disorders (concentration, mood)
Macrocytosis (increased MCV) and megaloblastic anemia at a more frank stage
Pregnancy: uncorrected deficit = risk of neural tube defects (NTDs) in the fetus

For a clear clinical overview, see the folate deficiency (MSD Manuals, EN).

Caution with vitamin B12

High doses of folic acid can correct anemia while masking a B12 deficiency. In case of macrocytosis/anemia, also evaluate B12 before high supplementation.

Tests and benchmarks

Serum folate: sensitive to recent intake. A low value suggests probable deficiency.
RBC folate (red blood cell folate): better correlated with stores; an RBC folate < 305 nmol/L indicates a deficit. Benchmarks in the NIH ODS fact sheet.
Plasma homocysteine: often elevated in B9/B12 deficit; useful as a complementary indication.
Complete blood count: macrocytosis (elevated MCV), megaloblastic anemia.
Pregnancy context: for population-level NTD risk reduction, WHO targets an RBC folate ≥ 906 nmol/L in women of childbearing age (see WHO recommendation).

DFE: dietary folate equivalents

Guidelines are often expressed in DFE (Dietary Folate Equivalents). 1 µg DFE = 1 µg food folate = 0.6 µg folic acid (fortified food/supplement with meal) = 0.5 µg (fasting). Reference: NIH ODS – DFE.

Folate-rich foods (and cooking losses)

Leafy vegetables (spinach, chard, arugula), broccoli, cabbage
Legumes (lentils, chickpeas, beans)
Liver (poultry), eggs, citrus, avocado
Fortified grain products (depending on products)

Folates are sensitive to heat and storage. Favor gentle/short cooking and consume quickly. For content per food: CIQUAL.

Doses and tolerance

Intakes to aim for (adults)

EFSA (PRI, DFE): ~330 µg DFE/day (adult), ~600 µg DFE/day (pregnancy), ~500 µg DFE/day (breastfeeding). See the EFSA DRV synthesis.
NIH ODS (RDA, DFE): 400 µg DFE/day (adult), 600 µg DFE/day (pregnancy), 500 µg DFE/day (breastfeeding) — detailed guidelines.

Upper limit (UL)

UL (adults): 1,000 µg/day of folic acid (from fortified foods/supplements, not naturally present folate), according to the NIH ODS fact sheet. EFSA broadly aligns with this order of magnitude in its DRV opinions.
Why: limit the risk of masking a B12 deficiency and adverse effects at very high doses.

Interactions and precautions

Anti-folate medications (e.g., methotrexate), trimethoprim, some anti-epileptics: possible interferences with folate metabolism (see "Interactions" sections of the NIH ODS fact sheet).
Alcohol, malabsorption (e.g., celiac disease), increased needs (pregnancy): increase deficit risk.

Practical advice

Anchor intake through diet (green vegetables + legumes). If needed, a moderate supplement (e.g., 400 µg DFE/day equivalent) can be discussed, especially peri-conceptionally (target 600 µg DFE/day total during pregnancy). Evaluate B12 if macrocytosis.

FAQ

Is serum testing sufficient? Useful, but influenced by recent intake. RBC folate better reflects stores.

"Natural" folate vs folic acid tablet? Guidelines are in DFE. Folic acid is better absorbed → 0.6 µg folic acid = 1 µg DFE with meal. See DFE.

Can you over-supplement? Avoid exceeding 1,000 µg/day of folic acid (UL). In some, high doses can mask a B12 deficit.

Who is most at risk? Pregnancy/breastfeeding, alcoholism, malabsorption, diets low in vegetables, anti-folate medications.