What methylated actually means

By Dr Conor Kerley, PhD, cardiovascular and nutrition researcher.

The word is on half the labels in the shop, and the finding that justifies it turns out not to be about your genes at all.

Walk into any health shop and pick up five bottles, and on two or three of them, somewhere near the top, you will find the word methylated. It is doing a great deal of work for a single adjective, since it signals the considered version, the one that costs more, the thing you are supposed to look for. Then ask the person holding the bottle what it means and almost nobody can tell you, which is an odd position for an industry to have talked itself into: a mark of quality attached to a concept nobody has ever explained to the people paying for it.

The concept is not difficult. Your body spends all day moving small chemical units called methyl groups around, onto DNA, onto proteins, onto the chemicals your nerves signal with, and folate is the delivery system that picks those units up and drops them where they are needed. Folic acid, the synthetic form in fortified bread and in most cheap supplements, cannot do that job as it comes; it has to be converted first, through a series of enzyme steps, into 5-methyltetrahydrofolate, which is the finished form that circulates in your blood and gets into your cells. On a label it appears as 5-MTHF, or methylfolate. So methylated means the conversion has been done already, outside you, before you swallow it. Methylcobalamin, the B12 in the same bottle, is one of the two forms your own cells make for themselves; whether swallowing it in that form gets more B12 into you than the ordinary form does has not been settled, so the argument on this page is about folate, where it has been tested. Which raises the obvious question of who cares, if your body performs that conversion perfectly well on its own.

We are surprisingly bad at this

The first of those steps, folic acid into something the body can begin to work with, is handled by an enzyme called dihydrofolate reductase, or DHFR, and in 2009 two researchers measured how well human liver does that job and set it beside how well a rat's does [1]. Gram for gram, the human enzyme managed less than two per cent of the rat's activity, and it varied roughly fivefold from one person to the next [1]. That is not a statement about a minority with an unlucky gene. It is a statement about our species, because we fortify flour, we recommend supplements and we build public health policy around a form of folate that human biochemistry processes slowly and unpredictably, and the rat in the next cage handles it better than you do.

That finding is the strongest argument for the methylated forms, and the useful thing about it is what it does not require. It needs no gene test, no 23andMe printout and no genetics of any kind, because methylfolate arrives past the bottleneck and there is nothing left for the slow enzyme to do.

None of which would matter if it made no measurable difference, and it has been tested directly. A trial in women compared methylfolate against the same daily amount of folic acid and measured plasma folate, which is simply how much folate is circulating in the blood at a given moment and is the standard way of telling whether a supplement is arriving at all [2]. Methylfolate roughly doubled it at the same dose. The trial included women carrying the common MTHFR gene variant and women without it, and the advantage turned up in both groups [2], which is what you would expect if the bottleneck is a human problem rather than a genetic one.

The second measurement is the one I find harder to unsee. Because that first step is so slow in us, some folic acid never gets converted at all and goes on circulating in the bloodstream still in its synthetic form, which is to say still in the form the body cannot yet use; researchers call it unmetabolised folic acid. The same trial went looking for it, and after the folic acid doses it showed up 75% of the time, against 8% of the time after the methylfolate doses [2]. Three doses in four of the ordinary form left something behind in the blood that had not been dealt with, and fewer than one in ten of the methylated doses did. Folate, vitamin B6 and vitamin B12 each contributes to normal homocysteine metabolism, and I would rather they got on with that without a queue of unconverted material backed up behind a slow enzyme.

A prediction from Coleraine

There is a fourth B vitamin in this story, and it comes with the best piece of reasoning I know in the field. Riboflavin, vitamin B2, makes the cofactor that holds the MTHFR enzyme together, MTHFR being the enzyme that performs the final step of producing methylfolate inside you, and some people carry a variant of the MTHFR gene, C677T, which leaves the enzyme less stable so that it tends to shed that cofactor. Look at that biochemistry long enough and it hands you a prediction: if riboflavin matters anywhere it should matter in the people carrying two copies of the variant, and do nothing whatever in everyone else, which is an unusually specific thing to claim in advance and an unusually easy one to be wrong about.

A group at Ulster University in Coleraine went and tested exactly that, splitting participants by genotype before the trial rather than after it. In 181 patients, riboflavin at 1.6 mg a day for 16 weeks moved blood pressure in the two-copy group, and the authors recorded that no response was observed in the other genotype groups [3]; a second trial in 91 people with two copies found the same thing [4], and a four-year follow-up in the same research line reported the effect persisting [5]. The prediction came first, then the test, and the test agreed, which is rarer in nutrition research than it ought to be. What stays with me is the dose, because 1.6 mg a day is roughly what you would get from food, where this literature usually delivers its interesting results on the back of pharmacy-sized ones. Riboflavin's own place on a label is elsewhere, since it contributes to the reduction of tiredness and fatigue, but that line of work is why it earns a considered slot in a B complex rather than an afterthought.

So: methylated. It is not a marketing prefix and it is not really about your genome. It means somebody looked at how poorly humans handle synthetic folic acid and decided to do the difficult step for you, before it ever reached the bottle.

References

1. Bailey SW, Ayling JE. The extremely slow and variable activity of dihydrofolate reductase in human liver and its implications for high folic acid intake. Proc Natl Acad Sci U S A. 2009;106(36):15424–15429. PMID 19706381.
2. Prinz-Langenohl R, Brämswig S, Tobolski O, et al. [6S]-5-methyltetrahydrofolate increases plasma folate more effectively than folic acid in women with the homozygous or wild-type 677C→T polymorphism of methylenetetrahydrofolate reductase. Br J Pharmacol. 2009;158(8):2014–2021. PMID 19917061.
3. Horigan G, McNulty H, Ward M, Strain JJ, Purvis J, Scott JM. Riboflavin lowers blood pressure in cardiovascular disease patients homozygous for the 677C→T polymorphism in MTHFR. J Hypertens. 2010;28(3):478–486. PMID 19952781.
4. Wilson CP, McNulty H, Ward M, et al. Blood pressure in treated hypertensive individuals with the MTHFR 677TT genotype is responsive to intervention with riboflavin: findings of a targeted randomized trial. Hypertension. 2013;61(6):1302–1308. PMID 23608654.
5. Wilson CP, Ward M, McNulty H, et al. Riboflavin offers a targeted strategy for managing hypertension in patients with the MTHFR 677TT genotype: a 4-y follow-up. Am J Clin Nutr. 2012;95(3):766–772. PMID 22277556.

Last reviewed: 10 September 2026. This article is educational and is not medical advice.