Supplements
Folate vs. Folic Acid: What MTHFR Testing Does and Does Not Tell You
The variant is real. The advice built on top of it has gotten far ahead of the evidence. Here is what folate, folic acid, and methylfolate each are, and what a test result actually changes.
Somewhere between a 23andMe download and a wellness clinic intake form, a lot of women have been handed the same piece of news. You carry an MTHFR variant. The advice that follows is usually the same too. Stop taking folic acid, switch to methylfolate, and treat the folic acid in your prenatal as something to avoid.
It is a tidy story. It is also mostly not what the research supports. The genetics are real, but the conclusions built on top of them have gotten far ahead of the evidence, and the folic acid being warned about happens to be the single most successful nutrient intervention in modern public health.
Here is what each of these words actually means, and what a test result does and does not change.
Folate, folic acid, and methylfolate are not the same molecule
Folate is the umbrella term for vitamin B9 in all its forms. It is the name for the family.
Food folate is the version that occurs naturally in lentils, beans, spinach, asparagus, avocado, and oranges. Folic acid is a stable synthetic form used in supplements and in fortified flour, pasta, rice, and cereal. Methylfolate, written in the research as 5-MTHF, is the form your body actually uses once it finishes processing any of the others (Scaglione, 2014).
Your body converts folic acid into methylfolate through a few enzyme steps. The last of those steps is run by an enzyme called MTHFR. That is the whole reason this gene ended up in the wellness conversation.
What folic acid actually prevents
This part matters, because it is the evidence the newer advice is asking you to set aside.
In 1991, a randomized double blind trial across 33 centers in seven countries followed 1,817 women who had already had a pregnancy affected by a neural tube defect, meaning a serious malformation of the brain or spine. Women who got folic acid had 72 percent fewer affected pregnancies than women who did not, and the other vitamins tested showed no protective effect (MRC Vitamin Study Research Group, 1991).
The following year, a randomized trial in Hungary asked whether the same thing held for women who had never had an affected pregnancy. Among 4,753 confirmed pregnancies, there were six neural tube defects in the group taking a trace element supplement and zero in the group taking a multivitamin with 0.8 mg of folic acid (Czeizel and Dudas, 1992).
That evidence is why the United States began adding folic acid to enriched grain products in 1998. Looking at 19 population based birth defect programs, the CDC estimated that fortification prevents about 1,326 neural tube defect affected births every year (Williams, 2015).
In 2023, the US Preventive Services Task Force reviewed all of it again and reaffirmed its strongest grade of recommendation. Everyone who is planning a pregnancy or could become pregnant should take a daily supplement containing 400 to 800 mcg of folic acid (US Preventive Services Task Force, 2023).
Note the form named in that recommendation. It is folic acid, because folic acid is the form the outcome trials used.
What the MTHFR variant actually does
The variant everyone talks about is called C677T, and it was first described in 1995 as a common change in the MTHFR gene (Frosst, 1995). Common is the right word. Plenty of people carry one copy, and a meaningful number carry two.
Carrying two copies does have a measurable effect. Using DNA and blood samples from 6,793 people in a national US health survey, researchers found that people with two copies had serum folate about 22 percent lower and homocysteine about 26 percent higher than people with no copies. Homocysteine is an amino acid that rises when folate processing is sluggish (Yang, 2008).
Then comes the part that rarely gets quoted. In that same analysis, a moderate daily folic acid intake, averaging about 150 mcg, significantly narrowed the homocysteine gap between the two genotypes. The variant made a difference mainly when folate intake was low.
Why geneticists stopped ordering the test
The MTHFR test became popular on a specific chain of reasoning. The variant raises homocysteine, high homocysteine causes clots and heart disease, so knowing your genotype should help predict clotting risk and recurrent miscarriage.
Larger analyses broke that chain. The American College of Medical Genetics and Genomics reviewed the evidence and concluded that meta-analyses had disproven both links, the one between high homocysteine and coronary heart disease and the one between MTHFR genotype and venous blood clots. Their guidance was direct. MTHFR testing has minimal clinical utility and should not be ordered as part of a routine workup for clotting disorders (Hickey, 2013). ACMG issued an addendum in 2020 that kept that position in place (Bashford, 2020).
So a professional body of medical geneticists looked at this gene and recommended testing it less, not more. That is unusual, and it is worth sitting with if a clinic has told you the opposite.
Does the variant mean you need methylfolate?
This is the honest middle of the topic, and it deserves a straight answer rather than a slogan.
Methylfolate is a legitimate form of the vitamin. In a randomized trial of 144 women aged 19 to 33 taking supplements for 24 weeks, methylfolate raised red blood cell folate more than an equivalent dose of folic acid did (Lamers, 2006). That is a real finding about a blood marker.
What no trial has shown is that methylfolate prevents more birth defects. The outcome data, the actual counted cases of spina bifida and anencephaly, sit with folic acid.
And folic acid does still work in people who carry the variant. In a randomized crossover trial, red blood cell folate rose with 400 mcg of folic acid across each MTHFR C677T genotype, including in people carrying the variant (Anderson, 2013). The enzyme is slower, not broken.
Which leaves a reasonable position. If you take a prenatal or a B complex containing methylfolate, that is fine. If you take one containing folic acid, that is also fine, and it is the form with the birth outcome evidence behind it. What is not supported is throwing out a folic acid prenatal because of a gene result, or paying for expensive methylfolate protocols sold on the promise that ordinary supplements cannot work for you.
The one real caution with folic acid
There is a genuine issue, and it has nothing to do with MTHFR. It involves vitamin B12.
Folate and B12 work together, and high folate intake can improve the anemia caused by B12 deficiency while the nerve damage keeps progressing quietly underneath. In an analysis of 1,459 older Americans, people with low B12 status who also had high serum folate were about three times as likely to have anemia and about two and a half times as likely to have cognitive impairment as people with low B12 and normal folate. In people whose B12 was normal, high folate was not associated with harm, and was actually linked with less cognitive impairment (Morris, 2007).
The takeaway is not to fear folate. It is to make sure B12 is on the radar too (our guide to who is actually low in B12 covers exactly this), particularly if you are over 65, vegan, or on long term metformin or acid blocking medication.
What to actually do
If you could become pregnant, take 400 to 800 mcg of folic acid daily, and start before conception rather than after a positive test, since the neural tube closes in the first few weeks. Eat folate rich food alongside it. Lentils, beans, spinach, asparagus, avocado, broccoli, and oranges all count.
If you already know you carry an MTHFR variant, you do not need a special protocol. Take a prenatal or a multivitamin with either folic acid or methylfolate, keep your intake steady, and know that steady intake is the thing that closes most of the genotype gap anyway.
If you are considering paying for MTHFR testing to explain fatigue, anxiety, or miscarriage, that money is better spent on the workup your doctor would actually act on. Ferritin, thyroid, B12, and a proper evaluation of recurrent pregnancy loss all lead somewhere. (We cover low iron and thyroid testing in their own guides.) A genotype that professional guidelines recommend against ordering usually does not. (For more calm looks at supplement claims, see our supplements section.)
When to see a doctor
Recurrent miscarriage, a personal or family history of blood clots, a previous pregnancy affected by a neural tube defect, or a diagnosis being managed with high dose folate all deserve a real clinician rather than a supplement decision made at the shelf. A previous affected pregnancy in particular changes the dose, and that is a prescription level conversation, not a guess.
References
- MRC Vitamin Study Research Group. Prevention of neural tube defects: results of the Medical Research Council Vitamin Study. The Lancet. 1991. PMID: 1677062
- Czeizel AE, Dudas I. Prevention of the first occurrence of neural-tube defects by periconceptional vitamin supplementation. The New England Journal of Medicine. 1992. PMID: 1307234
- Williams J, et al. Updated estimates of neural tube defects prevented by mandatory folic acid fortification, United States, 1995-2011. MMWR Morbidity and Mortality Weekly Report. 2015. PMID: 25590678
- US Preventive Services Task Force. Folic acid supplementation to prevent neural tube defects: reaffirmation recommendation statement. JAMA. 2023. PMID: 37526713
- Frosst P, et al. A candidate genetic risk factor for vascular disease: a common mutation in methylenetetrahydrofolate reductase. Nature Genetics. 1995. PMID: 7647779
- Yang QH, et al. Prevalence and effects of gene-gene and gene-nutrient interactions on serum folate and serum total homocysteine concentrations in the United States. The American Journal of Clinical Nutrition. 2008. PMID: 18614746
- Hickey SE, Curry CJ, Toriello HV. ACMG Practice Guideline: lack of evidence for MTHFR polymorphism testing. Genetics in Medicine. 2013. PMID: 23288205
- Bashford MT, et al. Addendum: ACMG Practice Guideline: lack of evidence for MTHFR polymorphism testing. Genetics in Medicine. 2020. PMID: 32533132
- Lamers Y, et al. Red blood cell folate concentrations increase more after supplementation with [6S]-5-methyltetrahydrofolate than with folic acid in women of childbearing age. The American Journal of Clinical Nutrition. 2006. PMID: 16825690
- Anderson CA, et al. Response of serum and red blood cell folate concentrations to folic acid supplementation depends on methylenetetrahydrofolate reductase C677T genotype. Molecular Nutrition and Food Research. 2013. PMID: 23456769
- Morris MS, et al. Folate and vitamin B-12 status in relation to anemia, macrocytosis, and cognitive impairment in older Americans in the age of folic acid fortification. The American Journal of Clinical Nutrition. 2007. PMID: 17209196
- Scaglione F, Panzavolta G. Folate, folic acid and 5-methyltetrahydrofolate are not the same thing. Xenobiotica. 2014. PMID: 24494987
Common questions
I have the MTHFR gene variant. Should I stop taking folic acid?
There is no good evidence that you should. In a randomized crossover trial, red blood cell folate rose in response to 400 mcg of folic acid across each MTHFR C677T genotype, including in people carrying the variant. The enzyme works more slowly, it does not stop working. Folic acid is also the form used in the trials that showed a 72 percent drop in neural tube defects and in the fortification program the CDC credits with preventing about 1,326 affected births a year. If you prefer a prenatal with methylfolate, that is a fine choice. Dropping folate supplementation altogether because of a gene result is not.
Is methylfolate better than folic acid?
Whether methylfolate is better than folic acid depends on what you mean by better. In a 24 week randomized trial in 144 women of childbearing age, methylfolate raised red blood cell folate more than an equivalent dose of folic acid did. That is a real advantage on a blood marker. But no trial has shown that methylfolate prevents more birth defects, and folic acid is the form with decades of outcome data behind it. Either form will get folate into you. Only one of them has the counted results.
Should I get tested for MTHFR?
The American College of Medical Genetics and Genomics recommends against ordering it as part of a routine workup for clotting disorders, and reaffirmed that position in a 2020 addendum. Their reasoning is that larger analyses disproved the links the test was supposed to predict, both between high homocysteine and coronary heart disease and between MTHFR genotype and venous blood clots. If you are chasing fatigue, anxiety, or miscarriage, tests like ferritin, thyroid, and B12, plus a proper recurrent pregnancy loss evaluation, will tell your doctor far more.
How much folic acid should I take if I could get pregnant?
The US Preventive Services Task Force recommends 400 to 800 mcg daily for everyone planning a pregnancy or who could become pregnant, and gave it their strongest grade in 2023. Start before conception rather than after a positive test, because the neural tube closes in the first few weeks. If you have already had a pregnancy affected by a neural tube defect, the dose is different and much higher, and that is a conversation with your doctor rather than a decision at the supplement shelf.
Can too much folic acid hide a B12 deficiency?
Too much folic acid hiding a B12 deficiency is the caution worth taking seriously, and it has nothing to do with MTHFR. High folate can improve the anemia that B12 deficiency causes while nerve damage continues underneath. In an analysis of 1,459 older Americans, those with low B12 status and high serum folate were about three times as likely to have anemia and about two and a half times as likely to have cognitive impairment as those with low B12 and normal folate. In people with normal B12, high folate was not linked to harm. So the answer is to keep an eye on B12, especially if you are over 65, vegan, or on long term metformin or acid blockers.
