What it measures.
Folate (vitamin B9) is critical for DNA and RNA synthesis, methylation reactions, and red blood cell maturation. RBC folate reflects tissue stores over 3-4 months, while serum folate shows recent intake. MTHFR gene variants reduce conversion to active methylfolate.
Serum folate reflects recent intake (days); RBC folate reflects tissue stores over 3-4 months. RBC folate is more reliable for assessing true status.
Why it matters.
Folate deficiency causes macrocytic anemia, elevated homocysteine, and neural tube defects in pregnancy. Suboptimal levels impair methylation affecting mood, energy, and detoxification. MTHFR variants may require methylfolate rather than folic acid.
Physiology.
Dietary folate is converted through several enzymatic steps to 5-methyltetrahydrofolate (5-MTHF), the active form. 5-MTHF donates methyl groups to convert homocysteine back to methionine. MTHFR enzyme catalyzes the final activation step—variants reduce this conversion by 30-70%.
Testing & preparation.
How to prepare
- No fasting required
- Note any folate/B-vitamin supplementation
- RBC folate preferred for accurate status assessment
When to test
Evaluating anemia, elevated homocysteine, pregnancy planning, or MTHFR concerns. RBC folate preferred for true tissue status.
How often
Annually; more frequently during pregnancy or treatment.
Interpretation.
High folate
Common causes:
- Folate supplementation
- Very rarely a concern
Implications:
- Usually not problematic
- High-dose folic acid may mask B12 deficiency
- Very high supplementation could theoretically impact B12 status
Low folate
Common causes:
- Dietary deficiency
- MTHFR variants (impaired activation)
- Alcoholism
- Malabsorption (celiac, IBD)
- Medications (methotrexate, anticonvulsants)
- Increased demand (pregnancy)
Implications:
- Macrocytic anemia
- Elevated homocysteine
- Neural tube defects in pregnancy
- Impaired methylation
- Depression, cognitive issues
- Increased cancer risk (long-term deficiency)
Optimization.
Diet
- Dark leafy greens (spinach, kale, collards)
- Legumes (lentils, chickpeas, black beans)
- Asparagus, broccoli, Brussels sprouts
- Fortified grains and cereals
- Liver and organ meats
Lifestyle
- Limit alcohol (impairs folate absorption)
- Address gut health for optimal absorption
- Consider genetic testing for MTHFR if concerned
Supplements
- Methylfolate (5-MTHF) preferred over folic acid
- 400-800 mcg daily for general supplementation
- Higher doses (1-5mg) for MTHFR variants or elevated homocysteine
- Always take with B12 to prevent masking deficiency
FAQs.
What's the difference between folate and folic acid?
Folate is the natural form found in food. Folic acid is the synthetic form used in supplements and fortified foods—it requires conversion through multiple enzymatic steps to become active methylfolate (5-MTHF). People with MTHFR variants have reduced ability to make this conversion. Methylfolate supplements bypass this issue, providing the already-active form that everyone can use directly.
Should I get tested for MTHFR?
MTHFR testing is optional. The C677T variant affects 10-15% of people (homozygous) and reduces enzyme activity by 30-70%. However, treating with methylfolate works regardless of genetic status. If you have elevated homocysteine, history of neural tube defect pregnancy, or poor response to folic acid, you might benefit from methylfolate supplementation without needing genetic confirmation.