What is methylation? A plain-English guide to how it works

What methylation means

Methylation is your cells attaching a methyl group, a tiny cluster of one carbon atom and three hydrogen atoms (CH₃), to another molecule. Those small tags work like switches on your DNA, proteins, neurotransmitters and hormones, turning their activity up, down, on or off.

It happens constantly, in almost every cell, and it runs on a steady supply of nutrients: folate, vitamin B12, vitamin B6, riboflavin (B2), choline and betaine. Your genes affect how efficiently you use them, which has made methylation a big talking point in DNA testing.

This article explains:

What methylation does in your body

Most methyl groups come from a single molecule, S-adenosylmethionine, usually shortened to SAMe. Your body makes SAMe from methionine, an amino acid found in protein foods, and a large family of enzymes called methyltransferases use it to hand methyl groups on.

Once SAMe has given away its methyl group, it becomes S-adenosylhomocysteine (SAH) and then homocysteine, which your body recycles back into methionine. That recycling step is where folate and B12 come in.

Methylation is also how you make creatine, which muscles and the brain use for quick energy, and phosphatidylcholine, a main building block of cell membranes. Between them, these two use up a large share of your daily SAMe.

The five methylation cycles

Methylation depends on a set of linked pathways rather than a single reaction. Stride's DNA test groups the genes involved into five cycles, and each one has its own in-depth article.

The folate cycle

This is where folate from food, or folic acid from supplements and fortified foods, becomes 5-MTHF, the active form that supplies the methyl group for recycling homocysteine. It also makes building blocks for new DNA, which is why folate matters so much in early pregnancy. MTHFR is the best-known gene here. Read more about the folate cycle.

The methionine cycle

The central loop. Methionine becomes SAMe, SAMe donates its methyl group, and the leftover homocysteine is turned back into methionine, either by the MTR enzyme using 5-MTHF and vitamin B12 or by BHMT using betaine. When people talk about the methylation cycle, this is usually the one they mean, and our methionine cycle guide walks through each step.

The transsulphuration pathway

Homocysteine that isn't recycled can leave the loop here. The CBS enzyme, with vitamin B6 as its helper, starts converting it into cysteine, which your body uses to make glutathione, one of its main antioxidants. There's more on this in our transsulphuration pathway article.

The BH4 cycle

BH4 (tetrahydrobiopterin) is a helper molecule your body needs to make serotonin, dopamine and nitric oxide. Its recycling is tied to folate metabolism. Stride's BH4 report also covers genes that break neurotransmitters down, including COMT, MAOA and MAOB, which we explain in the BH4 cycle.

The urea cycle

Your liver uses this cycle to turn ammonia, a by-product of breaking down protein, into urea for your kidneys to excrete. It shares the amino acid arginine with nitric oxide production, so Stride's report here looks at NOS3, which makes nitric oxide in blood vessel walls, and SOD2, an antioxidant enzyme. Read more about the urea cycle.

When we analysed more than 10,000 Stride methylation results, almost everyone had at least one inefficiency somewhere. Only about 2% had fully normal folate and BH4 function.

An impaired cycle on a genetic report is a tendency. It tells you where to pay attention, and it doesn't mean anything is wrong with you today.

Genetic methylation tests vs biological age tests

The word methylation turns up in the names of two very different kinds of test, and they're easy to mix up.

A genetic methylation test reads your DNA sequence. It looks for variants in the genes that make methylation enzymes, such as MTHFR, MTR and COMT. Your sequence doesn't change, so you only need to do it once.

An epigenetic test, often sold as a DNA methylation or biological age test, measures the methyl tags themselves at hundreds or thousands of sites across your DNA. Those tags shift with age and lifestyle, and algorithms called epigenetic clocks compare your pattern with reference data to estimate how old your body seems.

If you want to know whether your genes make folate and B12 more important for you, you need the genetic kind. If biological age is what interests you, an epigenetic clock is one way to estimate it. StrideOne takes another route, calculating Stride BioAge from blood biomarkers and tracking it over time (UK only).

What affects methylation

Genes set the starting point. Variants in MTHFR can reduce how much active folate you make, MTR and MTRR variants affect the B12-dependent recycling step, and FUT2 and TCN2 influence how well you absorb and transport B12. Most people carry a few of these, and each one usually has a modest effect on its own.

Nutrients matter at least as much. The cycles can't run without folate, B12, B6 and riboflavin, while choline and betaine provide a back-up supply of methyl groups.

Several other things can tip the balance:

• Alcohol. Regular heavy drinking reduces how much folate you absorb and store, and interferes with homocysteine recycling.

• Smoking. Smokers tend to have lower folate and higher homocysteine, and smoking leaves distinct changes in methylation patterns in the blood.

• Age. Methylation patterns drift as you get older (the basis of epigenetic clocks), and B12 absorption often falls in later life.

• Stress. Long-term stress has been linked to methylation changes in stress-response genes, although most of this research is still at an early stage.

• Medicines and nitrous oxide. Metformin and long-term proton pump inhibitors (PPIs) can lower B12 over time. Methotrexate deliberately blocks part of the folate cycle, which is why doctors often prescribe folic acid alongside it. Recreational nitrous oxide inactivates B12.

If you take any of these medicines, keep taking them as prescribed and ask your GP whether a B12 or folate check makes sense.

Signs methylation may be under strain

You can't feel methylation directly, and no symptom points to it on its own. Problems usually show up through what happens when folate or B12 run low, or when homocysteine builds up:

• tiredness that rest doesn't fix, sometimes with breathlessness or pale skin

• a sore, red tongue or mouth ulcers

• low mood, poor concentration or a foggy memory

• on a blood test, unusually large red blood cells (a high MCV) or raised homocysteine

These have many possible causes, so treat them as a reason to test rather than proof of a methylation problem. Some need prompt attention, because nerve damage from low B12 can become permanent. See your GP soon if you notice:

How to check your methylation

A DNA test and a blood test answer different questions, and they're most useful together.

DNA: your built-in tendencies

A genetic test shows which variants you carry and which cycles may need more support. The Stride DNA & Methylation Test uses an at-home cheek swab and reports on all five cycles at every level, with results in about 10 working days and a 1:1 consultation with an expert to talk them through. If you've already tested with 23andMe, you can upload your raw data instead.

Blood: what's happening now

Your genes can't tell you your current levels. These blood markers can:

• Folate reflects your recent intake.

• Active B12 (holotranscobalamin) is the share of B12 your cells can actually take up, and it can drop before total B12 does.

• Homocysteine shows how well recycling is working overall. It isn't part of most standard panels, so ask your GP.

Optimal Bloods (UK only) includes folate and active B12 among more than 70 biomarkers, but not homocysteine.

How to support methylation

Start with food. Spinach, broccoli, chickpeas and lentils provide folate, eggs are one of the richest everyday sources of choline, and beetroot and quinoa supply betaine. B12 comes from fish, meat, eggs and dairy, or from fortified foods if you're vegan. Our guide to supporting methylation naturally has a full food table, a sample day of meals and the habits that help most.

Supplements make most sense when your diet falls short or a blood test shows low folate or B12. Genetic results pointing to a slower folate or methionine cycle are another reason to consider them. Active forms such as methylfolate, methylcobalamin and B6 as P5P are already in the shape your body uses. MS-01 Methylation Support provides all three in one daily capsule, plus TMG and vitamin C. Folate, vitamin B6 and vitamin B12 contribute to normal homocysteine metabolism.

If MTHFR is the gene that brought you here, our MTHFR guide explains what C677T and A1298C mean and how folic acid fits in.

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