Frequency
About one person in two carries an MTHFR variant.
Liew & Gupta, 2015
Nutrilexic · Terrain & Genetics · MTHFR
MTHFR: the polymorphism that slows folate use
The variant you may carry without knowing
About one person in two carries a natural variant of the MTHFR gene. Think of a gene as a recipe your body reads to build a small tool, an enzyme. This tool's job: turn the vitamin B9 in your food into the form your cells can actually use, L-methylfolate. When the recipe runs a little slow, a whole inner workshop slows with it: making the messengers of mood, repairing DNA, clearing a waste product called homocysteine. The variant does not cause disease. It simply changes how you use vitamin B9.
Peer-reviewed sources, informed by the clinical experience of naturopaths.
Key takeaways
C677T
Most studied variant. Enzyme activity drops 30 to 70 % depending on combinations.
Frosst, Nat Genet 1995
Active B9
Prefer L-methylfolate over synthetic folic acid.
Stover & Field, 2011
Methylation
Homocysteine, neurotransmitters and DNA repair all depend on the cycle.
Bailey, J Nutr 2015
Not a disease
MTHFR is a polymorphism, not a pathology. Environment matters just as much.
Nutrilexic synthesis
The context
One enzyme, two variants, a thousand consequences
The two most studied variants are called C677T and A1298C. Picture them as two small typos in the gene's recipe, at very specific spots. Depending on whether you inherited it from one parent or both, the enzyme's output drops by 30 to 70 %. The practical consequence: the synthetic folic acid found in most standard supplements piles up unconverted, while your needs for the already-active form rise. Persistent fatigue, brain fog, anxiety, recurrent miscarriages, or a high homocysteine level on a blood test are the signals that drew researchers' attention.
Knowing your MTHFR status does not change everyone's plate, but it guides a few choices: prefer the already-active form of B9 (L-methylfolate) over synthetic folic acid, look after your intake of vitamin B12, choline (egg yolk, liver) and betaine (beetroot, spinach), and limit exposures that overload this circuit.
What science says
A polymorphism, not a disease
The literature clearly separates these common variants from rare genetic diseases. Carrying the C677T version on both copies of the gene (one from each parent) doubles the risk of a functional folate shortfall, but does not double the absolute risk of falling ill. Your environment, your plate and your status in other B vitamins matter just as much as the genetics itself.
The quiz below walks through the essentials in five progressive levels: what MTHFR is, how to measure it, what to do with it in practice.
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MTHFR and folates - Getting started
MTHFR and folates
Level 1/5 - Getting started
Our body transforms dietary folates, also called vitamin B9, into methylfolate, an active molecule essential for hundreds of cellular reactions. The MTHFR enzyme drives this transformation. But in one person out of two, a genetic variation slows it down. What we eat, and which form of B vitamin we take, can make a real difference. You can ask 3 questions across the whole exploration. Answers are generated by an AI drawing on reference scientific publications such as certified scientific publications, the Journal of Medical Genetics, the American Journal of Clinical Nutrition... See terms and conditions. The glossary in the footer expands on every term used.
This exploration is educational. It does not replace medical advice. Any active folate supplementation or treatment change should be discussed with a healthcare professional. Terms and conditions →
Sources
- Frosst P et al.. « A candidate genetic risk factor for vascular disease: a common mutation in methylenetetrahydrofolate reductase ». Nat Genet, 1995.
- Liew SC, Gupta ED.. « Methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism: epidemiology, metabolism and the associated diseases ». Eur J Med Genet, 2015.
- Stover PJ, Field MS.. « Trafficking of intracellular folates ». Adv Nutr, 2011.
- Bailey LB et al.. « Biomarkers of Nutrition for Development, Folate Review ». J Nutr, 2015.