TikTok Myth of the Week: Why Everyone’s Freaking Out About the MTHFR Gene

Did you know that a significant percentage of the U.S. population has one of the less-efficient variants of the MTHFR gene? TikTokers love to say this, and it’s true. They’ll also claim that if you have a MTHFR variant, that you need special vitamins, and that the wrong vitamins (or even some medications) will be toxic to you. This is not true, even though some influencers have built their entire online personalities around claims like these.

They’ll tell you that MTHFR (which TikTokers love to call the “mother f-er gene”) is responsible for your (or your child’s) autism, ADHD, depression, anxiety, thyroid issues, or other conditions. They’ll offer testing for the gene or for vitamin levels in your blood; they’ll also sell you coaching to guide you through the process of determining which supplements to take. And they will sell you supplements. So many supplements.

What is MTHFR, really?

In our bodies we have thousands of enzymes that each do one specialized little job, like a factory worker who puts in one specific bolt on each car that comes down the line. MTHFR is the name of both one of your enzymes (a little factory worker) and the gene that codes for it. We’ll talk about the gene in a minute, but first let me give you one short paragraph of biochemistry that you can skim if you aren’t in the mood.

So, here goes. MTHFR, or methylenetetrahydrofolate reductase, is an enzyme that converts 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofolate. This is necessary because 5-methyltetrahydrofolate goes on to donate a methyl group to homocysteine, making methionine. Methionine is an amino acid that we need to make protein, thus making it important for growth, cell division, and just generally for life.

This pathway involves more enzymes besides MTHFR, and it also involves a few chemical compounds that you know as vitamins. Vitamin B12 (cyanocobalamin) is also involved in this pathway. The molecule that MTHFR most directly acts on is a form of folate, a relative of folic acid, sometimes called vitamin B9. These vitamins are essential to our bodies because they are needed for biochemical pathways including this one.

What is the MTHFR gene, really?

The MTHFR enzyme only exists because our bodies build it, and the instructions to build it are contained in the MTHFR gene in our DNA. (You can think of a gene as a recipe; they often contain instructions for an enzyme or some other useful protein.)

You can see the MTHFR entry in the National Library of Medicine’s Gene database here. It resides on chromosome 1, in humans. (Other animals have their own versions.) It is expressed in many different tissues, including the lungs, thyroid, spleen, and more. We all have a MTHFR gene—two, actually, since we have two copies of every gene—but mine might not be identical to yours.

What are MTHFR variants?

There are different versions of MTHFR, as there are with many genes. People sometimes use the term “mutation,” but that isn’t really accurate, since that word implies a one-off, recent change. The different versions of MTHFR are more like hair colors or eye colors. You don’t have a brown hair “mutation,” you just have brown hair. Geneticists use the term variants for the different flavors of a gene.

There are versions of MTHFR that can do their methylating job pretty efficiently, and there are versions that are slightly less good at their job. The “slightly less good” variants are still functional and don’t cause any significant health issues in most people.

TikTokers will tell you that “44%” or “40% to 70%” or “over 50% of us” have one of the gene variants that makes a potentially less-efficient version of the enzyme, and they’re not wrong. Exactly how many of us have a MTHFR variant is hard to say; some of the variants only make a less-efficient enzyme when combined with another variant, or if you have two copies of, say, the T variant of the C677T SNP compared to two C’s or one of each. Some variants are also more common in some ethnic groups than others. But the bottom line is, MTHFR variants are extremely common.

And the fact that they’re so common should tell you something: If MTHFR variants were as devastating as TikTok implies, a medical understanding of them would be right out in the open, not something that you have to seek out special knowledge about. Something that affects half the population is, to use the technical meaning of the term, normal.

What TikTokers say MTHFR means

Many of the MTHFR videos on TikTok are in the same mold as the cortisol ones: lists of “symptoms” that range from common inconveniences to severe health problems, and recommendations about supplements and treatments.

The MTHFR videos funnel you pretty aggressively toward spending money on testing (either of your DNA or your vitamin levels) and especially toward supplements. Convincing people they have MTHFR issues, and then selling supplements and/or coaching to address those imaginary issues, is big business.

What’s wrong with having a MTHFR variant, according to these influencers? One pharmacist blames the gene for causing “headaches, inflammation, depression, infertility, GI problems, heavy periods, and your thyroid’s acting up.” (How you’re supposed to figure out that your thyroid’s acting up, he doesn’t say.)

A self-described MTHFR coach says that “ADHD, anxiety, autism, autoimmune issues, chronic fatigue, colon cancer, depression, digestive issues, hormonal issues, migraines, thyroid problems” are “all symptoms of the MTHFR genetic mutation.”

A naturopath blames MTHFR variants for depression, anxiety, and “poor detoxification,” saying it leads to “imbalances” in your neurotransmitters.

There are also a lot of cozy talking-head videos from people who say that they have struggled with MTHFR themselves. One mother blames MTHFR for her daughter’s speech delays and parasites, explaining how the girl’s small body is “overwhelmed with toxins” and that the gene predisposes her to “becoming an addict.” Another woman says the gene will “f you up” and that it’s the thing “no one tells you about, no one talks about.”

Does MTHFR actually cause health problems?

The only reason anybody knows about this gene is because its effect on health has been studied. To spoil the suspense: Nearly everything claimed above has zero basis in scientific literature, or the connections are so tenuous that scientists are not sure if they are linked to the gene or not.

One health condition linked to the gene is hyperhomocysteinemia, which may occur when you have certain MTHFR variants and you don’t get enough folate. Elevated levels of homocysteine were previously thought to be a risk factor for blood clots, stroke, and pregnancy loss. But ever since the U.S. mandated that grain products be fortified with folic acid, the association between MTHFR and those conditions has disappeared.

Another potential issue with MTHFR is the risk for neural tube issues in babies. Folate (vitamin B9) is important in early pregnancy so that the neural tube can develop properly, becoming the brain and spinal cord. In some populations, people with some MTHFR variants are more likely to have a baby with a neural tube defect than people with the more efficient form of the gene.

But here’s the important thing: no matter which MTHFR variant you have, taking extra folic acid solves the problem. The American College of Medical Genetics and Genomics and the American College of Obstetricians and Gynecologists both say that genetic testing for MTHFR is not necessary or useful, and that the recommended intake of folic acid (400 micrograms in addition to what you get in food, for a goal of 600 micrograms total) is plenty for everybody.

Don’t fall for the lie that you need “methylated” vitamins

One claim I saw repeatedly was the idea that if you have the MTHFR gene (by which they mean one of the potentially less-effective variants) that you should buy methylated vitamins, like 5-methyltetrafolate instead of regular folic acid. Many of the influencers will then go on to say that the un-methylated versions are “toxic” to you.

The claims get pretty wild from there. In one clip, a podcaster says she “literally feel[s] like [she’s] going to have a stroke” if she takes un-methylated B vitamins. Another TikToker, representing a genetic testing company, claims that “Methylfolate prevents neural tube defects. Folic acid doesn’t prevent anything.”

But that’s exactly backwards. Folate exists in many different forms in food and in your body. Some are more bioavailable than others, and some break down more easily in cooking or just while they’re sitting in the supplement bottle. Folic acid is the only supplement that has been shown to prevent neural tube defects in babies. Not methylfolate or any of the dietary folates. An article in the American Journal of Clinical Nutrition emphasizes this (I’ve added the bold formatting):

it has been suggested in both the popular media and the scientific literature that dietary folic acid should be replaced by the more “natural” 5-methyltetrahydrofolate for NTD [neural tube defect] prevention. These suggestions should be interpreted with caution because there is currently no evidence that 5-methyltetrahydrofolate can prevent NTDs, whereas it has been shown conclusively that folic acid supplementation reduces the risk of NTDs across diverse populations. Importantly, folic acid supplementation in women with the TT MTHFR genotype has been shown to increase folate status above that which is considered maximally protective for NTDs (9).

Do not, do not, do not take a non-standard vitamin just because a TikTok told you to (or because you got that information from a nutrition “coach” that you found through TikTok). If you are pregnant or considering becoming pregnant, take at least 400-600 micrograms of folic acid in supplements. (People who are not likely to get pregnant are still recommended to get the equivalent of 400 micrograms, but it’s not as critical whether that’s folic acid or another form of folate.)

By the time you know you’re pregnant, a lot of the critical steps in neural tube formation have already happened, so taking folic acid before pregnancy is recommended whenever possible. Since 1998, grain-based products (including most breads, cereals, etc) have contained extra folic acid, thanks to a U.S. law specifically designed to reduce the rate of neural tube defects. If you have previously had a baby with a neural tube defect, talk to your doctor about possibly taking a higher dose folic acid supplement.

Strangely, the MTHFR TikTokers also warn about the dangers of “over-methylating” if you take methylated vitamins. Your body does not walk a tightrope between “over” and “under” methylation, and there isn’t a general “methylation” process that affects everything in your body. As far as I can tell, the idea of undermethylators and overmethylators is a naturopath/wellness TikTok trope, and not something you’ll find in medical research.

MTHFR does not cause “stork bites” or other birthmarks

Another myth that gets repeated on TikTok is that common features of newborn babies’ appearance, like “stork bites,” “sugar bugs,” and sacral dimples, are signs that the baby has an MTHFR variant and is prone to certain health conditions. These birthmarks are not linked with MTHFR, although there wouldn’t be any reason for concern even if they were. Remember, MTHFR testing isn’t medically useful. There’s nothing your doctor would recommend doing differently if you know your child has a MTHFR variant.