MTHFR is a gene that provides instructions for making an enzyme your body needs to process folate (vitamin B9) and regulate an amino acid called homocysteine. About 30 to 40 percent of people carry at least one variant in this gene that reduces how well the enzyme works. Most of them never experience symptoms, but certain combinations of variants can affect everything from pregnancy outcomes to cardiovascular health.
What the MTHFR Gene Does
The MTHFR enzyme converts folate from the food you eat into its active form, called methylfolate. This active folate is the only form your body can actually use in a process called methylation, which is involved in DNA repair, neurotransmitter production, and breaking down homocysteine. Homocysteine is a normal byproduct of protein metabolism, but it needs to be recycled back into methionine (a useful amino acid) to keep levels in check. MTHFR makes that recycling possible by supplying the methyl group needed for the conversion. The enzyme also relies on B vitamins, including B2, B3, and B12, as helpers in this process.
When MTHFR works well, homocysteine stays within its normal range of 5 to 15 micromoles per liter. When the enzyme is sluggish, homocysteine can build up in the blood, and the downstream supply of methylfolate drops. That combination is what creates the potential health effects associated with MTHFR variants.
The Two Main Variants
Two common genetic variants affect the MTHFR gene: C677T and A1298C. You inherit one copy of the gene from each parent, so you can carry zero, one, or two copies of either variant.
C677T is the more studied and more impactful of the two. If you carry one copy (heterozygous), your MTHFR enzyme retains about 56 percent of its normal function. If you carry two copies (homozygous), enzyme function drops to roughly 20 percent. That’s a significant reduction that can meaningfully raise homocysteine levels, especially if your diet is low in folate.
A1298C has a milder effect. Carrying one copy generally doesn’t cause measurable changes in homocysteine. Carrying two copies may reduce enzyme activity, but the impact is less consistent across studies and doesn’t produce the same heat-sensitive instability seen with C677T. Some people carry one copy of each variant (compound heterozygous), which can have effects somewhere between the two.
Heart and Blood Vessel Risk
Elevated homocysteine is an independent risk factor for coronary artery disease, stroke, deep vein thrombosis, and pulmonary embolism. Because the C677T variant can raise homocysteine, researchers have studied whether carrying the variant directly increases cardiovascular risk. The connection is strongest in people who are homozygous for C677T and also have low folate intake, since adequate folate can compensate for the enzyme’s reduced efficiency. High homocysteine, high cholesterol, high LDL, and smoking have all been identified as independent predictors of coronary artery disease when analyzed together.
This doesn’t mean everyone with an MTHFR variant will develop heart problems. It means you have one additional factor to manage, primarily through diet and, if needed, supplementation.
Pregnancy and Neural Tube Defects
MTHFR variants have received significant attention in reproductive health. A large meta-analysis of 25 studies found that mothers homozygous for C677T (carrying two copies) had roughly double the risk of having a baby with a neural tube defect compared to mothers without the variant. Carrying one copy also raised the risk, though more modestly.
The good news is that folic acid supplementation appears to protect against neural tube defects even in women with C677T variants. The CDC recommends 400 micrograms of folic acid daily for anyone who could become pregnant, regardless of MTHFR status. This recommendation applies to folic acid specifically, not methylfolate supplements, because the evidence base for neural tube prevention was built on folic acid.
Links to Depression and Schizophrenia
MTHFR variants have a documented association with certain psychiatric conditions. A large meta-analysis published in Frontiers in Psychiatry found that people homozygous for C677T had a 66 percent higher risk of major depression and a 35 percent higher risk of schizophrenia compared to those without the variant. There was also a marginal link to bipolar disorder in the homozygous group.
The A1298C variant showed a different pattern. It wasn’t significantly associated with schizophrenia, but people homozygous for A1298C had nearly three times the risk of major depression compared to those without it. Interestingly, these associations varied by ethnicity. The links between MTHFR variants and depression or schizophrenia were strongest in Asian populations and less consistent in Caucasian populations.
The proposed mechanism is straightforward: reduced methylfolate means less raw material for producing neurotransmitters like serotonin and dopamine. This doesn’t mean an MTHFR variant causes depression on its own, but it may be one contributing factor among many.
Glutathione and Detoxification
You may have seen claims that MTHFR variants impair your body’s ability to detoxify. There’s a kernel of truth here, but the picture is more nuanced than many wellness sites suggest. Homocysteine sits at a metabolic crossroads. When it isn’t recycled back to methionine (the pathway MTHFR supports), it can alternatively be converted down a different route that produces cysteine, which is the building block your body needs to make glutathione, its primary antioxidant.
In theory, disrupting either pathway could affect glutathione levels. In practice, research in animal models with reduced MTHFR function found that glutathione levels in tissue didn’t drop significantly, because cells have backup systems for acquiring cysteine. So while MTHFR variants can shift the balance of these pathways, the body appears to compensate, at least partially, to maintain its antioxidant defenses.
Should You Get Tested?
Despite the popularity of MTHFR testing in integrative and functional medicine, the American College of Medical Genetics and Genomics (ACMG) issued a practice guideline stating there is a lack of evidence to support routine MTHFR polymorphism testing. Their position is that the variants are common, the clinical significance is limited for most people, and the result rarely changes medical management.
The reason is practical: whether or not you carry a variant, the recommended actions are largely the same. Eat a folate-rich diet, take folic acid if you’re planning a pregnancy, and check homocysteine levels if you have cardiovascular risk factors. A homocysteine blood test is more useful than MTHFR genotyping for most people, because it tells you whether the pathway is actually impaired rather than whether you have the theoretical potential for impairment.
Methylfolate vs. Folic Acid Supplements
One of the most common questions people have after learning about MTHFR is whether they should take methylfolate (5-MTHF) instead of standard folic acid. Methylfolate is the already-active form of folate, so it bypasses the MTHFR enzyme entirely. For people with significantly reduced enzyme function, this can be an advantage.
A bioavailability study found that in people homozygous for C677T, methylfolate had a longer-lasting effect on lowering homocysteine than folic acid. Six months after stopping supplementation, homocysteine levels remained significantly lower in the methylfolate group (12.1) compared to the folic acid group (16.9). That said, standard folic acid still works for most people with MTHFR variants, it just requires the enzyme to do more processing. For pregnancy planning specifically, the CDC still recommends folic acid over methylfolate based on the existing evidence.
Foods That Support Folate Levels
The recommended daily intake of folate is 400 micrograms for most adults, rising to 600 micrograms during pregnancy. Building a folate-rich diet is one of the most practical things you can do regardless of your MTHFR status. The top food sources include:
- Beef liver (3 ounces): 215 mcg, about 54% of the daily value
- Spinach (½ cup, cooked): 131 mcg
- Black-eyed peas (½ cup, cooked): 105 mcg
- Fortified breakfast cereals (one serving): 100 mcg
- Asparagus (4 spears, cooked): 89 mcg
- Brussels sprouts (½ cup, cooked): 78 mcg
Because the MTHFR enzyme also depends on B2, B3, and B12 to function, making sure you get adequate amounts of these vitamins supports whatever enzyme activity you do have. Staying well hydrated and eating a diet rich in colorful fruits and vegetables provides antioxidant support that can help offset oxidative stress, which further impairs methylation when left unchecked.