Understanding the MTHFR Gene: What It Is, What It Isn't, and Why It Matters

Over the past decade, the MTHFR gene has become one of the most talked about genes in health and wellness. Many people discover they have an MTHFR variant after completing genetic testing and immediately wonder if it explains years of fatigue, anxiety, hormonal problems, migraines or other health concerns.

The reality is a little more complex.

At Innate Biology, we believe understanding your genetics should empower you, not frighten you. Your genes provide a genetic instruction, not your destiny. Knowing how your body naturally functions allows you to make informed decisions about nutrition, lifestyle and targeted supplementation to support your unique biochemistry.

What is the MTHFR gene?

MTHFR stands for Methylenetetrahydrofolate Reductase, an enzyme that plays an important role in the body's methylation cycle.

Its main job is to convert dietary folate and folic acid into the active form of folate known as 5-methyltetrahydrofolate (5-MTHF).

This active folate is required for hundreds of essential processes throughout the body, including:

• DNA synthesis and repair
• Cell growth and division
• Healthy pregnancy and fetal development
• Production of neurotransmitters such as dopamine, serotonin and norepinephrine
• Detoxification pathways
• Conversion of homocysteine into methionine
• Formation of S-adenosylmethionine (SAMe), the body's primary methyl donor
• Healthy immune function
• Red blood cell production

Because methylation influences almost every cell in the body, reduced MTHFR activity may contribute to a wide variety of health concerns in some individuals.

The Two Most Common MTHFR Variants

Although hundreds of MTHFR variants exist, two are commonly included in genetic testing.

MTHFR C677T (rs1801133)

This is the most extensively researched MTHFR variant.

The change results in a less stable enzyme that works less efficiently, particularly when folate intake is low.

Approximate enzyme activity:

Normal (CC)
Approximately 100% activity

Single Variant (CT)
Approximately 60–70% activity

Double Variant (TT)
Approximately 20–35% activity

Individuals with two copies of the C677T variant generally have the greatest reduction in enzyme function and are more likely to develop elevated homocysteine if folate status is inadequate.

MTHFR A1298C (rs1801131)

This variant has a smaller effect on enzyme function than C677T.

Approximate enzyme activity:

Normal (AA)
Approximately 100%

Single Variant (AC)
Minimal reduction

Double Variant (CC)
Approximately 60–80% activity

Unlike C677T, A1298C does not usually increase homocysteine on its own but may influence neurotransmitter production and methylation when combined with other genetic variants or nutritional deficiencies.

What Does "Single" or "Double" Variant Mean?

We inherit one copy of every gene from each parent.

No Variant (Wild Type)
You inherited the common version from both parents.

Single Variant (Heterozygous)
One parent passed on the common version and one passed on the variant.

Double Variant (Homozygous)
Both parents passed on the same variant, resulting in a greater reduction in enzyme activity.

Some people inherit one copy of C677T and one copy of A1298C. This is known as compound heterozygosity, and enzyme activity is typically reduced to an intermediate degree.

Does Having an MTHFR Variant Mean You Will Become Sick?

No.

This is probably the biggest misconception surrounding MTHFR.

Many healthy people carry one or even two variants and never experience any obvious health problems.

Whether the variant affects you depends on many interacting factors, including:

• Dietary folate intake
• Vitamin B12 status
• Vitamin B2 (riboflavin)
• Vitamin B6
• Choline intake
• Stress
• Sleep
• Alcohol
• Smoking
• Gut health
• Other genes involved in methylation

Genetics load the gun, but lifestyle often pulls the trigger.

How Can Reduced MTHFR Activity Affect Health?

If methylation becomes less efficient over time, some people may be more susceptible to:

Cardiovascular Health

Reduced MTHFR activity may contribute to elevated homocysteine, particularly in people with the C677T TT genotype and low folate intake.

Persistently elevated homocysteine has been associated with an increased risk of cardiovascular disease, stroke and blood vessel dysfunction, although lowering homocysteine with supplements has not consistently reduced cardiovascular events in clinical trials.

Pregnancy

Adequate folate is essential before conception and during early pregnancy.

Women with reduced MTHFR activity may benefit from ensuring optimal folate status before pregnancy. Current obstetric guidelines still recommend adequate folate intake for all women planning pregnancy, regardless of MTHFR status. MTHFR variants alone are not considered a cause of recurrent miscarriage, and routine testing is not recommended by major obstetric organisations.

Mental Health

Methylation helps produce neurotransmitters including dopamine, serotonin and norepinephrine.

Reduced methylation may contribute to symptoms in susceptible individuals, although mental health is influenced by many genes and environmental factors.

Fatigue and Energy Production

Folate and vitamin B12 are essential for healthy red blood cell production and cellular energy metabolism.

Poor methylation may contribute to fatigue when accompanied by nutrient deficiencies.

DNA Repair

Folate is required for DNA synthesis and repair.

Long-term folate deficiency can impair normal cell division and increase genomic instability.

Supporting the MTHFR Pathway

Rather than trying to "fix" the gene, the goal is to provide the body with the nutrients it naturally requires.

Evidence-based strategies include:

• Eating plenty of naturally folate-rich foods such as leafy greens, asparagus, avocado, broccoli, Brussels sprouts and legumes.
• Maintaining adequate vitamin B12, particularly for vegetarians and older adults.
• Ensuring sufficient riboflavin (vitamin B2), which is required for optimal MTHFR enzyme activity. Studies suggest riboflavin supplementation may reduce blood pressure in some people with the C677T TT genotype.
• Consuming adequate vitamin B6, choline and other methylation nutrients.
• Supporting overall gut health to optimise nutrient absorption.
• Limiting smoking and excessive alcohol intake.
• Managing chronic stress, prioritising sleep and engaging in regular physical activity.

For some people, a practitioner may recommend 5-methyltetrahydrofolate (5-MTHF) instead of folic acid, particularly if there is documented folate deficiency or poor tolerance of folic acid. However, supplementation should always be individualised, as some people are sensitive to high doses of methyl donors.

One Gene Is Only One Piece of the Puzzle

One of the biggest mistakes in genetic interpretation is focusing on a single gene.

MTHFR works alongside many other genes involved in methylation, including MTR, MTRR, TCN2, SLC19A1, DHFR, PEMT, COMT, CBS, BHMT and FUT2. Looking at MTHFR in isolation provides only a small part of the picture.

This is why comprehensive DNA interpretation is far more valuable than simply knowing whether you have an MTHFR variant.

At Innate Biology, we assess how multiple genes interact with your nutrition, symptoms, lifestyle and health history to develop practical, personalised recommendations that support your body's unique biochemistry.

The Bottom Line

Having an MTHFR variant does not mean something is "wrong" with you.

It simply means your body may process folate a little differently.

For many people, this has very little impact. For others—particularly when combined with nutritional deficiencies, stress or additional genetic variants—it may contribute to reduced methylation efficiency.

The encouraging news is that nutrition, lifestyle and targeted support can often optimise these pathways. Understanding your genetics provides an opportunity to work with your biology rather than against it.

At Innate Biology, we believe your genes are not your destiny—they are your genetic instructions. The goal of genetic testing is not to diagnose disease, but to better understand how your body functions so you can make informed choices that support lifelong health.