Folate low — why methylated folate often beats standard folic acid
Serum folate below ~3 ng/mL (or RBC folate below ~150 ng/mL) marks frank deficiency; the 'low-normal' grey zone runs through ~7 ng/mL serum / ~300 ng/mL RBC. Folate is essential for one-carbon metabolism — it provides the methyl group that converts homocysteine back to methionine and supports DNA synthesis in dividing cells. Deficiency causes megaloblastic anaemia (large, immature red blood cells), elevated homocysteine, neural-tube defects in pregnancy, and a range of methylation-sensitive symptoms (low mood, fatigue, brain fog). Critically, ~30-40% of European-descent populations carry MTHFR C677T variants that impair conversion of dietary folic acid to active 5-MTHF — meaning standard folic acid supplementation is poorly utilised, and methylated folate (5-MTHF) is increasingly favoured in the literature.
Reference ranges
| Serum folate — frank deficiency | < 3 ng/mL |
| Serum folate — low-normal grey zone | 3 – 7 ng/mL |
| Serum folate — adequate | > 7 ng/mL |
| RBC folate — adequate | > 305 ng/mL |
What this marker measures
Serum folate reflects recent dietary intake (last few days). RBC folate reflects tissue folate status over the prior ~3 months (because RBC lifespan is ~120 days). For chronic-status assessment, RBC folate is more informative; for acute supplementation tracking, serum folate moves faster. The methylation-active form is 5-methyltetrahydrofolate (5-MTHF), produced from dietary folate (or supplemental folic acid) via the MTHFR enzyme. MTHFR variants reduce this conversion efficiency by 30-70%, so people with the variants often have 'normal' serum folate but functional deficiency.
Why might it be low?
- ·Inadequate dietary intake (low leafy greens, legumes)
- ·Alcohol intake (impairs folate absorption and metabolism)
- ·MTHFR variants reducing conversion to active 5-MTHF
- ·Methotrexate, anticonvulsants, sulfasalazine (folate antagonists)
- ·Coeliac, IBD, malabsorption
- ·Pregnancy and lactation (high demand)
- ·Haemodialysis
Why might it be elevated?
- ·Recent supplementation (no concern)
- ·Folic acid fortification effects
FAQ
5-MTHF vs folic acid?+
Folic acid is the synthetic form used in food fortification and most cheap supplements; it requires conversion via MTHFR before becoming active. 5-MTHF (Quatrefolic, Metafolin) is the bioactive form already used by the cell. For people with MTHFR variants — and quite possibly for everyone — 5-MTHF is the more reliable supplement form. Standard dose 400-1000 mcg daily.
Should I supplement folate alone or with B12?+
Always check B12 first. Folate supplementation with concurrent B12 deficiency can mask the haematologic signs of B12 deficiency (megaloblastic anaemia normalises) while neurological damage from B12 deficiency continues — a known clinical pitfall. The literature recommends B12 supplementation alongside any meaningful folate supplementation.
This page describes biomarker research and reference ranges for self-tracking and research-context discussion only. It is not medical advice, not a diagnosis, and not a substitute for a qualified physician. Take any concerns about your health to a clinician.
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