The MTHFR Gene: What Your Variants Mean for Folate

MTHFR (methylenetetrahydrofolate reductase) is one of the most studied genes in nutrigenomics. It produces an enzyme that converts folate into its active form, L-methylfolate, which your body uses for DNA synthesis, neurotransmitter production, and homocysteine metabolism.

The Key Variants

C677T (rs1801133)

This is the most clinically significant MTHFR variant:

• CC (normal): Full enzyme activity. Standard folate metabolism.
• CT (heterozygous): Enzyme activity reduced by about 35%. Mildly increased homocysteine levels.
• TT (homozygous): Enzyme activity reduced by up to 70%. Significantly elevated homocysteine.

About 10-15% of North Americans are homozygous TT. The frequency varies by ethnicity — it's more common in Hispanic and Mediterranean populations.

A1298C (rs1801131)

This variant has a milder effect:

• AA (normal): Full enzyme activity.
• AC (heterozygous): Slight reduction in activity.
• CC (homozygous): Moderate reduction, though less severe than C677T TT.

What To Do About It

If you carry one or two copies of the C677T variant:

1. Consider methylfolate supplementation. L-5-methylfolate (400-800 mcg daily for CT; 800-1000 mcg for TT) bypasses the MTHFR enzyme entirely.
2. Eat folate-rich foods. Dark leafy greens, lentils, and fortified foods help maintain folate levels.
3. Avoid folic acid in excess. Synthetic folic acid requires MTHFR to convert it. If your enzyme is impaired, unmetabolized folic acid may accumulate.
4. Monitor homocysteine levels. Ask your doctor to check serum homocysteine, especially if you're TT.

Important Context

Having an MTHFR variant does not mean you are unhealthy. It means your body may benefit from a different form of folate supplementation. Many people with TT genotypes live healthy lives with proper nutrition.

Always discuss supplementation with your healthcare provider, especially if you're pregnant or planning pregnancy, as folate is critical for neural tube development.