You may have come across the term MTHFR — usually buried in a parenting forum thread at 11pm, somewhere between sleep regression advice and opinions on screen time.
The full name is methylenetetrahydrofolate reductase, which is precisely as friendly as it sounds. But the basic concept is genuinely worth understanding — because it's surprisingly common, and it affects how the body processes certain B vitamins.
What Is MTHFR, in Plain English?
MTHFR is a gene that tells the body how to make a particular enzyme. That enzyme's job is to convert folic acid (vitamin B9) into its active form — methylfolate.
Methylfolate is involved in a process called methylation, which supports DNA repair, detoxification, neurotransmitter production and a long list of other things the body does quietly in the background. It happens constantly, in nearly every cell — one of those processes you never think about until something draws your attention to it.
Everyone has two copies of the MTHFR gene — one from each parent. In some people, one or both copies carry a variation that affects how efficiently this conversion happens.
Think of it like a kitchen tap. For most people, it runs at full flow. For others, it's slightly restricted — still works, just not quite as freely.
How Common Is It?
More common than you'd expect.
Estimates suggest that up to 40% of the population carry some form of MTHFR variation ᵃ. Most people have no idea — it doesn't always cause obvious symptoms, and it's rarely tested for routinely.
The two most studied variations are:
C677T — associated with reduced enzyme activity. Those with two copies (one from each parent) may produce significantly less methylfolate than those without the variation ᵇ.
A1298C — also associated with reduced function, though typically to a lesser degree.
Having one copy of either variation usually has a modest effect. Having two copies — or one of each — can have a more noticeable impact on how folate is processed.
What Does This Actually Mean Day-to-Day?
For most people, an MTHFR variation doesn't cause dramatic problems. But it can affect how efficiently the body uses folate — which plays a role in energy, mood, focus and cellular repair.
Research has explored associations between MTHFR variations and a range of health outcomes. This is still an evolving area of science, and having a variation doesn't mean any particular outcome is written in stone. It simply means the body may handle certain nutrients a bit differently.
The practical takeaway? For some people — particularly those with two copies of a variation — the form of folate and B12 they consume may matter more than it does for others.
Folic Acid vs Methylfolate: The Bit Worth Knowing
This is where it gets genuinely practical.
Folic acid is the synthetic form of folate — the one added to fortified foods (cereals, bread, flour) and found in most standard supplements. For the body to use it, folic acid must be converted into methylfolate. And that conversion relies on the MTHFR enzyme.
If that enzyme isn't running at full capacity, unmetabolised folic acid can build up while active methylfolate stays low. Not ideal.
Methylfolate (5-MTHF) is the already-active form. It doesn't need converting, which means the body can use it directly — regardless of what's going on with MTHFR.
This is why some supplements now use methylfolate instead of folic acid, and why methylated forms of B12 (methylcobalamin) and B6 (pyridoxal-5-phosphate) are sometimes preferred. It's not marketing fluff — for some people, the form genuinely matters.
Foods Naturally High in Folate
Whole foods contain folate in forms the body can generally use well. No conversion drama required.
Good sources include:
- Leafy greens (spinach, romaine, Swiss chard — good luck with that negotiation)
- Broccoli and asparagus
- Avocado
- Bananas
- Lentils and chickpeas
- Eggs
- Nuts, particularly hazelnuts
- Liver (for the adventurous)
Building these into regular meals supports folate intake without relying on fortified or synthetic sources. Even if half of them get pushed to the side of the plate.
Should You Test?
Home genetic tests for MTHFR are available, though they're not cheap — some cost upwards of £200–£375.
Testing can be useful if you have a specific reason to investigate. But many practitioners suggest that supporting methylation through diet and appropriate supplement forms makes sense regardless of whether you know your genetic status.
If you're curious, a simple mouth swab test can identify MTHFR variations. But knowing your status doesn't change the core advice: prioritise whole food sources of folate, and if you supplement, consider forms that don't rely on conversion.
The Bigger Picture
MTHFR variations are common — not rare, not alarming, and definitely not a diagnosis.
What they offer is a useful lens for understanding why some people may benefit from paying closer attention to the form of B vitamins they consume. And why "just take a multivitamin" isn't always the full answer.
For most families, this doesn't require genetic testing or a complete dietary overhaul. It's simply worth knowing that not all folate is created equal — and that the body's ability to use it varies from person to person.
One of those quiet details that can make a small but meaningful difference, once you know it's there.
Come and say hello
There's a growing community of fellow saints on Instagram—come say hello. Or leave your email, and we'll drop into your inbox now and then with things worth reading.
This is general information, not medical advice. If you have questions about your child's health, your GP or a registered healthcare professional is always the right place to start.
References
(a) Wilcken B, et al. (2003). Geographical and ethnic variation of the 677C>T allele of MTHFR. Journal of Medical Genetics. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1735493/
(b) Frosst P, et al. (1995). A candidate genetic risk factor for vascular disease: a common mutation in MTHFR. Nature Genetics. https://pubmed.ncbi.nlm.nih.gov/7647779/
(c) Rai V. (2016). MTHFR C677T polymorphism and susceptibility to ADHD. Neurological Sciences. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8073588
(d) Gilbody S, et al. (2007). MTHFR genetic polymorphism and psychiatric disorders. American Journal of Epidemiology. https://academic.oup.com/aje/article-abstract/165/1/1/232658
(e) Lewis SJ, et al. (2006). MTHFR genotype and cognitive function. British Journal of Nutrition. https://pubmed.ncbi.nlm.nih.gov/18154909/
(f) Wan L, et al. (2018). MTHFR C677T polymorphism and risk of congenital heart defects. Medicine. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6570969
(g) Smith AD, et al. (2008). Is folic acid good for everyone? American Journal of Clinical Nutrition. https://pubmed.ncbi.nlm.nih.gov/18689377/
Authorised nutrition and health claims are listed separately in the page footer.
