MTHFR, C677T & A1298C: what your result actually means
It's the most-Googled gene in consumer genetics, and the most over-sold. Here's the version without the panic.
MTHFR is the enzyme that switches folate on. Whatever folate you eat, plus the folic acid added to fortified bread and packed into cheap supplements, gets turned into 5-methylfolate, and that's the form your body can actually use to recycle homocysteine and keep methylation running. Two common variants make the enzyme work slower. They aren't a disease. Most people carry one. What they do change is which form of folate is the smarter buy for you.
What MTHFR does
Your cells need folate in its active form to build DNA and keep the methylation cycle turning. MTHFR handles the last step that activates it. When the enzyme runs slow, you convert folic acid less efficiently, so you end up carrying more leftover unmetabolised folic acid and making less of the active stuff your body wants.
The fix is simple. Take folate that's already in its active form, L-methylfolate (you'll also see it written as 5-MTHF), and you skip the slow step entirely. That's really the only practical reason to know your MTHFR status.
Your variants, decoded
This is the variant everyone studies. The T allele builds an enzyme that's slower and falls apart in heat.
| GG | Typical activity. Nothing to change here. |
| GA | One copy. Roughly a third less enzyme activity. |
| AA | Two copies. Activity drops a lot, and this is where switching to methylfolate makes the most sense. |
The second common one. Gentler by itself, and mostly studied next to C677T rather than alone.
| TT | Typical activity. |
| TG | One copy. Activity is a little lower. |
| GG | Two copies. Still only a little lower. |
Genotypes are shown order-insensitively and on the forward strand; your own export may print the complementary letters — the meaning is the same.
What the research suggests
Your MTHFR C677T variant slows the enzyme that activates folic acid. Methylfolate comes pre-activated, so it goes straight past that slow step and gives you a folate your genotype can actually use.
Your MTHFR A1298C variant trims folate-activating capacity a little; it usually runs alongside the better-studied C677T. Methylfolate is already activated, so it skips the slow conversion, and people who carry these variants tend to see a bigger drop in homocysteine when they take methylfolate.
PubMed 38892484 · MTHFR genotype & methylfolate homocysteine response
You carry two copies of MTHFR C677T, and that version of the enzyme leans harder on its riboflavin (B2) cofactor to stay stable. In 677TT people specifically, riboflavin has been shown to lower blood pressure. It's a cheap, low-risk addition next to methylfolate.
PubMed 27170501 · riboflavin lowers BP in MTHFR 677TT
Educational only — not medical advice. “General evidence” means the finding is real but the supplement’s benefit isn’t unique to your genotype.
See this matched to your own DNA — free.
Upload your 23andMe or AncestryDNA file and get your actual MTHFR result, plus every other actionable variant — each line cited, your file never stored.
Questions
Is an MTHFR variant dangerous?
By itself, no. These are common variants that a big chunk of the population carries. They shift which form of folate your body uses most easily. They are not a diagnosis.
Should I take folic acid or methylfolate?
If you carry C677T or A1298C, methylfolate (5-MTHF) is already activated and skips the step your enzyme struggles with. For most people in that boat, it's the better pick.