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Folate (vitamin B9)

Folate is a B vitamin your body needs for DNA synthesis, cell division and blood production.

What is Folate (vitamin B9)?

Folate (vitamin B9) is a water-soluble B vitamin the body cannot make itself. It is essential for DNA synthesis and cell division. Red blood cells must renew rapidly; when folate is insufficient they become too large and immature — a pattern called macrocytic anaemia visible in the blood count. Laboratories typically measure serum folate, which responds to recent food intake. Measure it fasting for a reliable result. Erythrocyte folate is more stable and reflects body stores over the past two to three months — more informative, but less routinely measured.

Why is Folate (vitamin B9) relevant?

Folate is critical in early pregnancy, when the embryo's neural tube closes. A deficiency at that stage raises the risk of serious birth defects — before most women know they are pregnant. Women planning a pregnancy are advised to start supplementation weeks before conception. Outside pregnancy, folate matters for blood cell production and the methylation cycle. Chronic heavy alcohol use, certain medications (including methotrexate and long-term proton pump inhibitors), and poor gut absorption reduce the level. A raised homocysteine — a marker linked to cardiovascular risk — is sometimes the first sign of a functional folate deficiency, even when serum folate still appears normal.

Folate (vitamin B9) high or low — what it means

Measure serum folate fasting: a recent meal containing leafy greens or fortified foods can temporarily inflate the value and mask a deficiency. Always read folate alongside vitamin B12. Both deficiencies produce a similar blood count pattern (macrocytic anaemia), but the treatment differs fundamentally. Supplementing with folic acid alone when a B12 deficiency goes unrecognised can temporarily improve the blood count while neurological damage from the B12 deficiency continues. Rule out B12 deficiency before starting high-dose folic acid. Add homocysteine to your test when functional folate reserve is in doubt — an elevated homocysteine confirms a cellular deficiency.

Folate (vitamin B9) reference ranges

DeficiencyClear folate deficiency; risk of macrocytic anaemia< 5 nmol/L
BorderlineSuboptimal; dietary or supplement adjustment advisable5-7 nmol/L
NormalAdequate serum folate for most adults (Dutch labs often use 7-40 nmol/L)> 7 nmol/L
Target when planning pregnancyHigher target around conception to protect neural tube development> 13 nmol/L
Red-cell folate (deficiency)Reflects stores over the past 2-3 months; the cut-off varies by assay, < 340 nmol/L is the WHO deficiency threshold< 340 nmol/L

Cut-offs differ by lab and assay; serum folate responds strongly to recent food intake (measure fasting). Based on the anaemia indicator, the WHO uses: deficiency < 6.8, possible deficiency 6.8-13.4, and normal 13.5-45.3 nmol/L. Always read folate alongside vitamin B12. The range on your own lab report is authoritative. Reference points, not a diagnosis.

Educational information only — not medical advice. Consult a healthcare professional for clinical decisions.

Read about our scientific approach →Read the guide: Energy →

Frequently asked questions

What is a normal folate level?

For adults, a serum folate above 7 nmol/L is generally considered normal, and Dutch labs often use 7-40 nmol/L. Between 5 and 7 nmol/L is borderline (suboptimal), and below 5 nmol/L indicates a clear deficiency. The WHO uses slightly wider bands (deficiency < 6.8, normal 13.5-45.3 nmol/L). Cut-offs vary by laboratory, so the reference range on your own result is what counts.

What does a low folate level mean?

A value below roughly 5-7 nmol/L points to a (developing) deficiency that disrupts red blood cell production. This can cause macrocytic anaemia (large red cells, MCV above 100 fL), with fatigue and problems with concentration and mood. Causes include a one-sided diet, alcohol, poor gut absorption, and certain medications (such as methotrexate). Always read a low folate alongside vitamin B12, because the treatment differs fundamentally.

What folate level should I aim for when planning a pregnancy?

When trying to conceive, a higher target above 13 nmol/L is recommended, because folate is critical for closure of the neural tube in the first weeks. Start 400 micrograms of folic acid per day around four weeks before planned conception and continue until about week 10, even if your current blood level looks normal.

When is a folate deficiency a concern?

It becomes concerning below 5 nmol/L, especially alongside symptoms or an abnormal blood count (large, immature red cells). An elevated homocysteine can confirm a functional deficiency even when serum folate still looks normal. Always rule out a vitamin B12 deficiency before taking high-dose folic acid: it can mask the blood abnormality while neurological B12 damage continues. A persistently low or unexplained result warrants a doctor's assessment.

Related biomarkers

Vitamin B12
Vitamin B12 is a B vitamin your body needs for your nerves, DNA production, and blood formation.
Homocysteine
Homocysteine is an amino acid your body clears with B-vitamins, rising when folate or B12 runs short.
Methylmalonic Acid (MMA)
Methylmalonic acid (MMA) is a metabolite that builds up when your cells run short on vitamin B12.
Erythrocytes (RBC Count)
Erythrocytes are your red blood cells, and the RBC count measures them per volume of blood to gauge oxygen transport.
Ferritin
Ferritin is the protein that stores iron in your cells, making it the most reliable blood test for your iron stores.
Hematocrit
Hematocrit is the percentage of your blood made up of red blood cells, your measure of oxygen-carrying capacity.

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