MTHFR: The Gene 40% of People Have and What It Actually Does

MTHFR is a gene that codes for an enzyme that converts folic acid into methylfolate — the active form of folate your body can actually use. Roughly 40% of people carry a variant that makes that conversion less efficient, which is why the folic acid in a multivitamin or fortified cereal may not be doing what you think. If you've seen MTHFR mentioned by a practitioner, on a supplement label, or while Googling "why doesn't folic acid work for me," here's what it actually means.

What MTHFR actually is

MTHFR stands for methylenetetrahydrofolate reductase. It's an enzyme, coded by a gene with the same name, that converts folic acid (the synthetic form found in most supplements and fortified foods) into methylfolate, the active form your body can actually use.

Methylfolate is essential. Your body needs it for DNA repair, neurotransmitter production, detoxification, and a process called methylation that quietly runs hundreds of functions behind the scenes.

Why it matters

Roughly 40% of people carry a variant in the MTHFR gene that reduces this conversion. Some variants slow it down a little. Others reduce efficiency significantly, meaning the folic acid in your multivitamin or your fortified cereal may not be doing what you think it's doing.

This doesn't mean something is "wrong" with you. It means your body has a specific preference for how it receives folate, and once you know that, you can work with it.

What this looks like in real life

People with reduced MTHFR activity often do better with methylfolate (the already-converted form) instead of folic acid. It's a simple switch, but it can make a noticeable difference in energy, mood, and overall function, especially for people who've been taking B-complex vitamins for years and never felt a thing.

This is also one of the reasons prenatal vitamin formulas have started shifting toward methylfolate. For women with MTHFR variants, it's not just a better option; it's the one their body can actually use.

The bigger picture

MTHFR doesn't work in isolation. It feeds into your methylation cycle, which connects to detoxification, hormone metabolism, and neurotransmitter balance. Understanding your MTHFR status gives you a clearer picture of how those systems work together in your body. It's one gene, but it touches a lot.

The bottom line

MTHFR is one of the most well-studied genes in nutrigenomics, and one of the most actionable. Knowing your status helps you choose the right form of folate, support your methylation pathways, and make informed decisions with your healthcare provider.

Your Mosaic report includes your MTHFR activity level as part of the Detoxification Pathways section, along with your overall methylation efficiency. It's one of 108 personalized insights across 9 areas of your health, all from a single cheek-swab sample.