What is MTHFR? The Gene Variant Affecting 40% of People

MTHFR stands for methylenetetrahydrofolate reductase — an enzyme, and the gene that codes for it. It sits at a single, narrow point in your metabolism, and when it works slowly, the effects ripple outward.

What the enzyme actually does

The MTHFR enzyme performs one job: it converts 5,10-methylenetetrahydrofolate into 5-methyltetrahydrofolate (5-MTHF), the active, usable form of folate. That form is then needed to recycle homocysteine back into methionine, which in turn produces SAMe — the body's principal methyl donor.

Methyl donors are used constantly: building neurotransmitters, regulating gene expression, producing glutathione, maintaining myelin. So a bottleneck at MTHFR is not a folate problem in isolation. It is a supply problem for the whole methylation cycle.

The two common variants

Two single-nucleotide polymorphisms account for most of what people mean when they say they "have MTHFR":

• C677T — the better-studied of the two. One copy is associated with modestly reduced enzyme activity; two copies (homozygous) with a substantially larger reduction.
• A1298C — generally associated with a smaller effect on its own, though carrying one copy of each variant (compound heterozygous) is common.

Estimates vary by population, but a large share of people carry at least one copy. That is why MTHFR is better thought of as ordinary human variation than as a rare finding.

How it shows up

Reduced MTHFR activity is associated with elevated homocysteine, since the recycling pathway depends on 5-MTHF. Homocysteine is a measurable blood marker, and it is the most objective handle most people have on their methylation status — far more useful than symptoms alone. Our guide to high homocysteine covers testing and interpretation.

Beyond that, experience varies widely between individuals — see the MTHFR spectrum and signs of impaired methylation.

Why the form of your B vitamins matters

Because the variant impairs a conversion step, supplying folate in a form that still requires that conversion — folic acid — does not resolve the bottleneck. Methylated B vitamins supply 5-MTHF, methylcobalamin and P-5-P already in their active forms, so the impaired step is bypassed rather than pushed harder.

The full explanation of the difference is in active vs inactive B vitamins, and if you're pregnant or planning to be, methylfolate vs folic acid in pregnancy is the relevant read.

Getting tested

MTHFR status is determined by a genetic test; homocysteine by a standard blood test. Your GP can order the latter. Many people start there, since it reflects what the pathway is currently doing rather than what your genes predispose it to do.

NeuroThrive™ products are food supplements and are not intended to diagnose, treat, or cure any medical condition. Genetic variants are not a diagnosis. Consult your GP before beginning any new supplement programme.