Vitamin B9 (Folate / Folic Acid)

VitaminFoundational

Needed every time a cell divides, and a partner to B12 in methylation.

At a glance

Essential

Builds new cells Supplies the building blocks for DNA. why ↓
Builds red blood cells Without it, cells come out large and dysfunctional. why ↓
Keeps homocysteine down Works with B12 to recycle homocysteine. why ↓
Protects pregnancy Lowers the risk of neural tube defects. why ↓

Strong human evidence

How to take it

About 400 mcg a day (600 in pregnancy)
Spinach, lentils, asparagus, avocado
L-5-MTHF if you have an MTHFR variant

Watch out

Synthetic folic acid: stay under 1,000 mcg a day
Too much folic acid can mask a B12 deficiency

Signs you're low

Fatigue, anemia
Sore tongue

The Research

Mechanisms, studies and evidence grades for each claim above.

Functions

DNA/RNA synthesis (cell division)
Red blood cell production
Methylation and homocysteine metabolism, alongside B12 and B6

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Mechanism

Works through one-carbon carriers (THF/5-MTHF), supporting thymidylate and purine synthesis, and feeding the B12-dependent conversion of homocysteine back to methionine. This is the pathway the Metabolic Health hub's L-5-MTHF supplement entry bypasses directly for people with a documented folate gap or MTHFR variant.

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Intake

RDA roughly 400 mcg DFE/day for adults; ~600 mcg DFE/day in pregnancy. Upper limit for synthetic folic acid is 1,000 mcg/day (adults).

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Deficiency effects

Megaloblastic anemia, fatigue, glossitis; elevated homocysteine. In pregnancy, increased risk of neural tube defects. Neurologic symptoms point toward B12 deficiency rather than folate alone — worth distinguishing since they're often discussed together.

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Excess effects

Excess folic acid may mask an underlying B12 deficiency, delaying diagnosis.

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Top foods

Spinach
Lentils
Asparagus
Avocado

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