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Clinical Diagram · Folate Metabolism · MTHFR · Fortification

The Folate Pathway —
Why synthetic folic acid
isn't the same as folate

Two routes to the same destination. One works for everyone. One requires a conversion step that up to 60% of the population cannot complete efficiently. Hover over any element for clinical detail.

↓ The diagram ↓ MTHFR variants ↓ Clinical notes

Select your MTHFR status to see enzyme efficiency

MTHFR enzyme efficiency: 100% — full conversion capacity
The Folate Pathway — Synthetic vs Food-Form · Hover for detail
Food folate pathway — active, direct
Synthetic folic acid pathway — requires conversion
MTHFR enzyme — the conversion bottleneck
Downstream methylation outputs
Blocked / accumulation pathway
SYNTHETIC FOLIC ACID PATHWAY FOOD FOLATE PATHWAY ⚠ UK FLOUR — MANDATORY 2024 Synthetic Folic Acid PTEROYLMONOGLUTAMIC ACID Bread · Flour · Most supplements DHFR enzyme · step 1 of 3 Dihydrofolate (DHF) INTERMEDIATE · STEP 1 DHFR enzyme · step 2 of 3 Tetrahydrofolate (THF) INTERMEDIATE · STEP 2 MTHFR enzyme · critical step MTHFR Methylenetetrahydrofolate reductase EFFICIENCY: 100% COFACTOR B2 · Riboflavin successful conversion UMFA Unmetabolised Folic Acid ACCUMULATES IN BLOODSTREAM Folate receptor competition ↓ NK cell activity Potential cognitive risk at low B12 Food Folate DIETARY POLYGLUTAMATE FORMS Spinach · Lentils · Liver · Avocado Asparagus · Broccoli · Chickpeas BYPASSES DHFR no MTHFR bottleneck Gut absorption cleaves chain enters as THF 5-MTHF 5-Methyltetrahydrofolate THE ACTIVE FORM ✓ METHYLFOLATE SUPP. enters here directly Methylation Cycle Homocysteine → Methionine → SAM 200+ DOWNSTREAM REACTIONS DNA repair · Neurotransmitters Oestrogen detox · Myelin · Glutathione Phospholipids · Histamine clearance COFACTOR B12 methylcobalamin VS HOVER OVER ANY ELEMENT FOR CLINICAL DETAIL

Clinical Context

What this means in practice

The diagram above shows the mechanism. These notes translate it into clinical decisions.

The fortification problem
Why adding folic acid to flour is not the same as adding folate
Mandatory UK folic acid fortification (2024) adds synthetic pteroylmonoglutamic acid to white and wholemeal flour. For the 40–60% of the population carrying MTHFR variants, this synthetic form cannot be efficiently converted. It accumulates as UMFA rather than reaching the methylation cycle as 5-MTHF. The policy was designed on population averages and does not account for this genetic variation.
What actually works
Food folate and methylfolate supplementation bypass the bottleneck
Natural food folate enters the pathway downstream of the DHFR/MTHFR conversion steps — it does not require MTHFR to become active. Supplemental methylfolate (5-MTHF) enters directly as the active form. Both are appropriate regardless of MTHFR status. For MTHFR variant carriers, switching from folic acid supplements to methylfolate removes the conversion dependency entirely.
Testing consideration
Genetics tells you the risk — plasma testing tells you the reality
MTHFR genetic testing (C677T, A1298C) identifies variant status but cannot tell you whether methylation is actually impaired. Two people with identical variants can have completely different functional methylation capacity depending on B2 status, dietary folate intake, B12, stress load, and gut absorption. The Methylation Profile Plasma (SAM, SAH, methylation index) measures the functional output directly. See the methylation plasma test →
The B12 dependency
5-MTHF cannot re-enter the cycle without adequate B12
Even when 5-MTHF is available, the remethylation step (homocysteine → methionine) requires B12 as methylcobalamin. B12 deficiency traps folate as 5-MTHF — the "methyl trap". This is why assessing B12 alongside folate status matters — and why cyanocobalamin (the synthetic B12 form in most supplements) is less reliable for MTHFR carriers than methylcobalamin or hydroxocobalamin.
Who is most affected
The populations where this matters most
MTHFR variants are most clinically significant in: women of reproductive age (recurrent miscarriage, neural tube defect risk); people with psychiatric or neurodevelopmental presentations (depression, anxiety, OCD, ADHD, schizophrenia); those with elevated homocysteine; people on medications that deplete folate cofactors (methotrexate, PPIs, OCP, anticonvulsants); and anyone consuming high amounts of fortified flour products.
Practical guidance
What to do if you carry MTHFR variants
1. Switch folic acid supplements to methylfolate (5-MTHF). 2. Maximise dietary folate from leafy greens, legumes, liver. 3. Reduce fortified flour product consumption where practical. 4. Ensure adequate B2 (riboflavin — MTHFR cofactor) and B12 (methylcobalamin preferred). 5. Consider functional testing to confirm methylation status rather than assuming a problem based on genetics alone.
Blog Post
Folic Acid Fortification: What They're Not Telling You
Blog Post
MTHFR, Methylation & Mental Health
Diagram
The Methylation Cycle — Full Interactive Diagram
Test
Methylation Profile Plasma — From £419
Testing Guide
Methylation Testing — All Options Explained