The short version
- In the MRC Vitamin Study, 1,817 women at high risk were randomised around conception and folic acid produced a 72% reduction in neural tube defects, relative risk 0.28 (95% CI 0.12 to 0.71), while seven other vitamins showed no significant effect.
- The US Preventive Services Task Force reaffirmed in 2023 that all persons planning or capable of pregnancy should take 400 to 800 micrograms of folic acid daily, its strongest recommendation grade.
- In 142 women randomised for 12 weeks, L-5-methyltetrahydrofolate raised red blood cell folate higher than folic acid, 1951 versus 1498 nmol/L, but both lowered homocysteine by a similar 15 to 17% with no significant difference between them.
- The American College of Medical Genetics and Genomics concluded in 2013 that MTHFR polymorphism testing has minimal clinical utility and should not be ordered as part of a routine thrombophilia evaluation.
- Folic acid is the synthetic oxidised form used in fortification and in the trials; methylfolate is the circulating form that skips the body's conversion steps.
Two things are true at once here, and most content on this subject picks one and ignores the other.
The first is that folic acid is the single best-evidenced supplement in the entire category. The second is that a large amount of what gets sold under the word "methylated" is trading on a genetic story that a professional genetics body has specifically recommended against testing for. Holding both at once is the honest position.
Start with the trial that settled it
The MRC Vitamin Study ran across 33 centres in seven countries and randomised 1,817 women at high risk of a neural tube defect pregnancy — because they had already had one — to folic acid, seven other vitamins, both, or neither. Among the 1,195 completed pregnancies with a known outcome, there were 27 neural tube defects: 6 in the folic acid groups and 21 in the groups without it. That is a 72% protective effect, relative risk 0.28 (95% CI 0.12 to 0.71). The other vitamins did nothing measurable (relative risk 0.80, 95% CI 0.32 to 1.72).
Note what was tested. Not methylfolate. Not a food-first approach. Synthetic folic acid, the cheap oxidised form, given before conception. That result is why grain fortification exists and why the US Preventive Services Task Force reaffirmed in 2023 that everyone planning or capable of pregnancy should take 400 to 800 micrograms of folic acid daily — an A recommendation, the strongest grade it issues.
What the two forms actually are
Folate is the family name for the compound as it occurs in food — leafy greens, legumes, liver. Folic acid is the synthetic, fully oxidised form used in fortification and most supplements. It is more stable and better absorbed, but it has to be reduced by the body to become usable. 5-methyltetrahydrofolate, sold as methylfolate or L-5-MTHF, is the circulating form, which skips those conversion steps.
Does skipping the steps matter? A 12-week randomised trial in 142 healthy Malaysian women compared 1mg of folic acid, an equimolar dose of L-5-MTHF, and placebo. Both raised folate status far above placebo. The methylfolate arm reached higher red blood cell folate than the folic acid arm — 1951 versus 1498 nmol/L (P = 0.003) — and higher plasma folate. On homocysteine, the functional readout, both groups fell about the same amount, 17% and 15% below placebo, with no significant difference between them.
That is a fair summary of the whole methylfolate case. It raises the marker more. It has not been shown to do more.
The MTHFR part, said plainly
MTHFR is the gene coding for the enzyme that produces 5-MTHF. The C677T variant is genuinely common and genuinely reduces enzyme activity. From there the marketing makes a leap: that carriers cannot process folic acid, need methylfolate specifically, and should be tested to find out.
The American College of Medical Genetics and Genomics published a practice guideline in 2013 on exactly this. Its conclusion: recent meta-analyses have disproven an association between hyperhomocysteinemia and coronary heart disease risk, and between MTHFR polymorphism status and venous thromboembolism risk. There is growing evidence that MTHFR polymorphism testing has minimal clinical utility and should not be ordered as part of a routine thrombophilia evaluation.
That guideline is about thrombophilia workups, not about prenatal nutrition, and it is worth being precise about the scope rather than overstating it. But it is the clearest professional statement available on whether the test tells you something actionable, and the answer is no.
So which should you take?
If you are pregnant or planning to be: take the form your care provider recommends, and take it. The intervention with the 72% effect size behind it is folic acid at 400 to 800 micrograms. Methylfolate is a reasonable alternative that raises blood folate at least as well, and if a clinician has recommended it for you there is no reason to argue. What is not defensible is delaying supplementation while you order a gene test.
If you are not pregnant and not planning to be, the honest answer is that most people in a fortified-grain country are not short of folate and do not need a standalone supplement of either form. It is one of the entries worth reviewing when you cut your stack. Both forms turn up inside a prenatal vitamin anyway, which is where the dose usually belongs.
What we'd actually tell you
The word "methylated" is doing a lot of work on supplement labels right now, and some of it is legitimate chemistry and some of it is a price premium attached to a genetics claim that the genetics profession has declined to endorse. Neither form is a scam. Neither is a breakthrough. If cost is a factor, folic acid is the one with the trial behind it.
Good questions
Is methylfolate better than folic acid?
It raises blood folate more, and has not been shown to do more. In a 12-week randomised trial, methylfolate reached higher red blood cell folate than an equivalent dose of folic acid, but both lowered homocysteine by a similar amount with no significant difference. Folic acid is the form with the neural tube defect trial behind it.
Should I get tested for MTHFR before choosing a folate supplement?
No. The American College of Medical Genetics and Genomics concluded that MTHFR polymorphism testing has minimal clinical utility and should not be ordered in a routine thrombophilia evaluation. It is not a test that changes what you should take. If you are planning a pregnancy, starting folic acid now matters far more than the result of a gene panel.
How much folic acid should I take if I'm trying to conceive?
The US Preventive Services Task Force recommends 400 to 800 micrograms daily for everyone planning or capable of pregnancy, and it graded that recommendation A. Start before conception, because the neural tube closes very early. Your own care provider may recommend a higher dose if you have a personal or family history, and that conversation should happen with them.
Can I get enough folate from food instead?
Possibly for general health, and not reliably for pregnancy prevention timing. Leafy greens, legumes and liver are genuinely rich sources, but the trial evidence for preventing neural tube defects used a supplement at a specific dose taken before conception, which is hard to guarantee from diet. Outside of pregnancy planning, most people in a fortified-grain country are not short.
Is the methylated version worth paying extra for?
Usually not on the evidence. Both forms raise folate status well and both lowered homocysteine similarly in a head-to-head trial. If methylfolate is what your prenatal contains, or what your clinician recommended, keep taking it. If you are choosing between two products and the only difference is the word methylated and the price, the cheaper one has the stronger trial record.
Do I need a folate supplement at all if I'm not planning a pregnancy?
For most people, no. Folate deficiency is uncommon in countries that fortify grain products, and there is no general case for a standalone supplement of either form. Some medications and some medical conditions change that, so if you have been told you need one, that advice is specific to you and this article is not.
Sources
- MRC Vitamin Study Research Group. Prevention of neural tube defects: results of the Medical Research Council Vitamin Study. Lancet, 1991. View study
- US Preventive Services Task Force. Folic Acid Supplementation to Prevent Neural Tube Defects: US Preventive Services Task Force Reaffirmation Recommendation Statement. JAMA, 2023. View study
- Henderson AM, Aleliunas RE, Loh SP, et al. l-5-Methyltetrahydrofolate Supplementation Increases Blood Folate Concentrations to a Greater Extent than Folic Acid Supplementation in Malaysian Women. J Nutr, 2018. View study
- Hickey SE, Curry CJ, Toriello HV. ACMG Practice Guideline: lack of evidence for MTHFR polymorphism testing. Genet Med, 2013. View study
These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.
