Vitamin B9 (Folate)

Your intake

What each level of vitamin b9 (folate) does

Approximate dose-response bands. Individual response varies — these are starting points, not prescriptions.

1. Severely lowYOU ARE HERE

   0 mcg – 132 mcg

   Risk of neural tube defects in pregnancy, megaloblastic anemia, elevated homocysteine.

2. Insufficient

   132 mcg – 400 mcg

   Methylfolate (5-MTHF) is the active form most useful for MTHFR variants.

3. Adequate

   400 mcg – 600 mcg

   DV (400 mcg DFE) met. Critical for methylation, DNA synthesis, and red blood cell formation.

4. Therapeutic

   600 mcg – 800 mcg

   Pregnant people often need 600–800 mcg DFE; check with provider.

5. High

   800 mcg – 1000 mcg

   Approaching the 1000 mcg supplemental UL — can mask B12 deficiency.

6. Over upper limit

   1000 mcg – +

   Above UL — may mask B12 deficiency and contribute to unmetabolized folic acid in circulation.

Overview

Folate is a B vitamin essential for one-carbon transfer in DNA synthesis, methylation, and amino acid metabolism. Adequacy in early pregnancy prevents neural tube defects — one of the highest-leverage micronutrient interventions in public health. Folic acid (synthetic) and 5-MTHF (natural active form) have important practical differences.

Functions

• ●Carries one-carbon units for purine and thymidylate synthesis (DNA)
• ●Converts homocysteine to methionine (methylation cycle)
• ●Required for hematopoiesis
• ●Critical for embryonic neural tube closure (days 21–28)

Mechanism

Folate enters the cell as 5-MTHF, donates a methyl group to homocysteine via methionine synthase (B12-dependent), and re-enters the cycle as THF. THF is reloaded with one-carbon units from serine and recycled through MTHFR back to 5-MTHF. MTHFR 677T variants reduce enzyme efficiency — folate demand rises in homozygotes.

Benefits

• ●Periconception folic acid (400 mcg/day) reduces neural tube defect risk by 50–70%
• ●Lowers homocysteine when combined with B12 and B6
• ●Reduces megaloblastic anemia
• ●May modestly reduce stroke risk in folic-acid-naïve populations (CSPPT trial)

Deficiency

Reduced sharply by mandatory grain fortification (1998 in US), but still common in pregnancy, alcoholism, malabsorption, and on certain medications.

Excess

Folic acid above 1,000 mcg/day can mask B12 deficiency anemia while neurological damage progresses unchecked. Possible link between unmetabolised folic acid in serum and immune effects — clinical significance debated.

Forms

• Folic acid
  Synthetic; stable; the fortification form; requires DHFR-mediated reduction
• Folinic acid (5-formyl-THF, leucovorin)
  Bypasses DHFR; used as methotrexate rescue
• 5-methyltetrahydrofolate (5-MTHF, methylfolate, Metafolin)
  Active circulating form; bypasses MTHFR
• Dietary folate (mixed polyglutamates)
  Natural food form; deconjugated to monoglutamate in gut

Food sources

• Beef liver (cooked) · 3 oz215 mcg DFE
• Lentils (cooked) · 1/2 cup180 mcg DFE
• Cooked spinach · 1 cup260 mcg DFE
• Asparagus (cooked) · 1/2 cup135 mcg DFE
• Avocado · 1 medium165 mcg DFE
• Fortified bread · 1 slice60 mcg DFE

Supplement forms

Methylfolate (5-MTHF, L-methylfolate) is the active form and bypasses the MTHFR step. For routine prenatal use, folic acid in the standard 400–800 mcg range remains the most clinically validated. Always pair high-dose folate with B12 — folate alone can mask B12 deficiency and let neurological damage progress.

Bioavailability

Folic acid is ~85% bioavailable; food folate is ~50% (hence the DFE conversion: 1 mcg food folate = 0.6 mcg folic acid taken with food). High doses of folic acid saturate DHFR, producing unmetabolised folic acid in serum — uncertain long-term significance. 5-MTHF is absorbed and used directly.

Longevity relevance

Adequacy reduces cardiovascular risk markers (homocysteine) and prevents major birth defects — both serious long-horizon benefits. Excess from over-fortification + supplements is the modern concern; aim for adequacy through food when not pregnant.

Relationships

References

• NIH ODS — Folateguideline
• Linus Pauling Institute — Folatereview
• MRC Vitamin Study — folate and NTDs (Lancet 1991)study
• CSPPT — folic acid and stroke (JAMA 2015)study

About Vitamin B9 (Folate)

One-carbon metabolism; DNA synthesis, methylation, red blood cell formation.

Role

DNA synthesis

Daily target

400 mcg (DV)

Upper limit

1000 mcg

Also called

folate, folic acid, vitamin b9, vitamin b-9, methylfolate, 5-mthf

Forms with lower absorption: folic acid. Prefer better-absorbed forms when supplementing.