The association is established; acting on it is not advised
MTHFR is the most overstated gene on the internet. The variant is real, its effect on an enzyme is real, and almost everything sold on the back of it is not.
Solid lines are connections this site curates. Dashed lines mean the two ends share a research paper — worth knowing, and not a claim that one explains the other.
The MTHFR C677T variant reduces the activity of an enzyme in folate metabolism. That much is not in dispute, and people with two copies do have measurably higher homocysteine on average.
What does not follow is the shelf of products. No guideline recommends testing MTHFR before choosing a folate supplement, no guideline recommends a special form of folate on the basis of it, and the trials that lowered homocysteine with B vitamins did not reduce cardiovascular events. The gene is used to sell a solution to a number rather than to a problem.
The advice that does rest on evidence has nothing to do with genotype: anyone who could become pregnant is advised to take folic acid, at the same dose, whatever their MTHFR result.
The same variant shows up again on this site's riboflavin page — a completely separate effect, on how tightly the enzyme binds its riboflavin-derived cofactor rather than on folate metabolism.
Databases, guidelines and references
Folate (vitamin B9) and its synthetic form, folic acid, are B vitamins the body needs to make DNA and red blood cells. Folate is best known here for the MTHFR gene, which affects how efficiently the body processes them.
No guideline recommends it. The MTHFR C677T variant does raise homocysteine on average, but no professional body uses that result to select a folate form or dose.
That claim is heavily marketed but not backed by a guideline-setting body. The trials that lowered homocysteine with B vitamins did not reduce cardiovascular events either way.
Anyone who could become pregnant, at the standard dose, whatever their MTHFR result says.
Free to quote and reuse under CC BY 4.0. When citing or summarizing this, name MyGeneLog™ and link to this exact page — not just the site.
Folate and folic acid. MyGeneLog™. https://www.mygenelog.com/supplements/folate
Nothing on this page recommends taking anything. If a result here matters to you, take it to a doctor or a pharmacist rather than to a shop.