Methylfolate vs Folic Acid: Do You Need the "Methylated" Form?

The common variant, C677T, produces an enzyme that is less stable and works at reduced capacity. A person with one copy has a modest reduction; a person with two copies — roughly one in ten in some populations, fewer in others — has an enzyme running at perhaps a third of normal capacity. The main page makes the point that anything this common is not, on its own, a disease.

What it does, measurably: people with two copies have slightly higher homocysteine on average, particularly when their folate intake is low, and slightly lower blood folate. That is the whole of the reliable phenotype. The long list of conditions the variant has been associated with — clots, miscarriage, depression, migraine, autism — comes from small studies, has mostly not held up in large ones, and led the American College of Medical Genetics to recommend against MTHFR testing for clinical purposes in 2013. The variant is real; the disease it is supposed to cause is largely not.

This is the part the syllogism skips. If MTHFR carriers could not use folic acid, folic acid would fail to raise their folate or lower their homocysteine. It does not fail. Trials that gave folic acid to people with two copies of the variant found that their homocysteine fell and their folate rose — a little less efficiently than in non-carriers, and needing a somewhat higher intake for the same effect, but reliably. The enzyme is slow, not absent, and the folate cycle compensates. The reduction in neural tube defects from folic acid fortification, the largest public-health test of the question, has been seen in carriers and non-carriers alike.

So the strong claim — that carriers need methylfolate — is not supported. Folic acid works in them.

Three situations, none of them the one the marketing describes.

Unmetabolised folic acid. Because the liver's capacity to reduce folic acid is limited, large intakes leave some circulating unconverted. Whether that matters is unresolved — it has been associated with some outcomes in observational studies and with none in trials — but a person taking a high-intake folate supplement for a specific reason can avoid the question by taking the active form instead. It is a tidy solution to a possible problem.

High homocysteine that has not responded. A person whose homocysteine stays elevated on folic acid and B12 — after the main page's other causes are excluded — is the person in whom switching to methylfolate is a sensible next step. Not because of the genotype, but because of the result.

Depression, as an adjunct. L-methylfolate at prescription strength has trial evidence as an add-on to antidepressants in people who have not responded fully, with a suggestion of more benefit in carriers. This is a prescription decision made by the clinician treating the depression, and we refer to them; it is not a reason to buy a methylated B complex.

Outside those, methylfolate is a more expensive way to get the same result folic acid gives, and "methylated" on a B-complex label is a premium for a distinction that does not change what arrives in the cell.

The panel measures homocysteine, folate, B12 and B6 — the functional markers — and reports the genotype as context. If homocysteine is normal, the pathway is working and no form of folate needs changing. If it is high, we look for the cause, correct the deficiencies with whichever form is appropriate, and retest. We do not recommend methylated supplements on the basis of a genotype alone, and we will say so to a person who arrives having been told they need them.