Folate
Vitamin B9
Essential B vitamin critical for cell division, DNA synthesis, and neural tube development. MTHFR gene variants affect ~40% of the population, making methylfolate (5-MTHF) the preferred form.
What is Folate?
Folate (vitamin B9) is a water-soluble B vitamin essential for one-carbon metabolism, DNA synthesis and repair, red blood cell maturation, and neural tube development during embryogenesis.
Known Health Benefits
How It Works
Folate in its active form, tetrahydrofolate (THF), functions as a one-carbon carrier in critical biosynthetic pathways. Through a series of interconversions, THF derivatives donate or accept single carbon units for purine and thymidylate synthesis — the building blocks of DNA and RNA. 5,10-methylenetetrahydrofolate is reduced by MTHFR (methylenetetrahydrofolate reductase) to 5-methylTHF (5-MTHF), the predominant circulating form. 5-MTHF donates its methyl group to homocysteine via methionine synthase (a B12-dependent reaction), producing methionine and regenerating THF. Methionine is then converted to S-adenosylmethionine (SAMe), the universal methyl donor for DNA methylation, histone modification, neurotransmitter synthesis, and phospholipid metabolism. MTHFR gene polymorphisms (C677T and A1298C) reduce enzyme activity by 30–70%, leading to decreased 5-MTHF production and elevated homocysteine. This explains why methylfolate (5-MTHF) bypasses the MTHFR bottleneck and is the preferred supplemental form for affected individuals.
What Research Says
The landmark MRC Vitamin Study (Lancet, 1991) demonstrated that periconceptional folic acid supplementation (4 mg/day) reduced neural tube defect recurrence by 72%, leading to mandatory folic acid fortification of grain products in the US since 1998. Post-fortification surveillance showed a 26% reduction in neural tube defects nationally. A meta-analysis by Blom et al. (Clinical Chemistry and Laboratory Medicine, 2011) confirmed that folate supplementation lowers homocysteine by 25%, though the Heart Outcomes Prevention Evaluation (HOPE-2) trial showed homocysteine lowering reduced stroke risk by 25% but did not significantly reduce overall cardiovascular events. The MTHFR C677T polymorphism affects 10–15% of North Americans in homozygous form and up to 40% heterozygously. Studies by Prinz-Langenohl et al. (AJCN, 2009) showed that 5-MTHF increased plasma folate more effectively than folic acid in women with MTHFR 677TT genotype.
Active Compounds
5-methyltetrahydrofolate (5-MTHF), folic acid, folinic acid
Forms & Bioavailability
Folic acid from supplements has approximately 85% bioavailability on an empty stomach and 100% when added to fortified food compared to ~50% for food folate. 5-MTHF has comparable bioavailability to folic acid and does not require MTHFR conversion.
Dosage Guidance
| Use Case | Dosage |
|---|---|
| General health | 400–800 mcg DFE/day |
| Preconception and pregnancy | 400–800 mcg 5-MTHF or folic acid daily |
| MTHFR variant support | 400–1000 mcg 5-MTHF/day |
| Homocysteine reduction | 400–800 mcg/day with B12 and B6 |
| Neural tube defect prevention (high risk) | 4000 mcg/day |
Always consult a healthcare provider for personalized dosing.
Natural Food Sources
- Dark leafy greens (spinach, kale, collards)
- Lentils and beans
- Asparagus
- Avocados
- Broccoli
- Liver (chicken or beef)
- Fortified grains and cereals
Potential Side Effects
May mask B12 deficiency at high doses; possible concern with unmetabolized folic acid
Who Should Avoid It
- Undiagnosed B12 deficiency (folate can mask hematological signs while neurological damage progresses)
- Concern about unmetabolized folic acid (UMFA) accumulation at doses >200 mcg folic acid
- Certain cancers where folate may promote cell growth (use only under physician guidance)
- Antifolate therapy (methotrexate) — supplementation may reduce drug efficacy
Pregnancy & Lactation
Folate is the single most important vitamin for pregnancy, as it prevents 50–70% of neural tube defects when taken periconceptionally (400–800 mcg/day starting 1+ month before conception). The RDA is 600 mcg DFE during pregnancy and 500 mcg during lactation. Women with MTHFR variants should use methylfolate instead of folic acid.
Known Drug Interactions
Methotrexate, phenytoin, and sulfasalazine may deplete or block folate
Evidence Classification
Supported by randomized controlled trials (RCTs), systematic reviews, or meta-analyses published in peer-reviewed journals.
Frequently Asked Questions
What is the difference between folic acid and methylfolate?
Folic acid is a synthetic form that must be converted to active 5-MTHF through several enzymatic steps including the MTHFR enzyme. Methylfolate (5-MTHF) is the biologically active form that bypasses MTHFR entirely. About 40% of the population has MTHFR variants that impair folic acid conversion, making methylfolate the preferred form.
What is MTHFR and should I be tested?
MTHFR (methylenetetrahydrofolate reductase) is an enzyme that converts folate to its active form. The C677T and A1298C variants are common and reduce enzyme activity by 30–70%. Testing is worthwhile if you have elevated homocysteine, recurrent pregnancy loss, neural tube defect history, or family history of MTHFR variants. Regardless of test results, methylfolate is a safe and effective choice.
How much folate do I need during pregnancy?
The standard recommendation is 400–800 mcg daily starting at least one month before conception and continuing through the first trimester. Women with a previous neural tube defect pregnancy should take 4000 mcg daily under medical supervision. Continue a prenatal with 400+ mcg throughout pregnancy.
Can folate mask a B12 deficiency?
Yes. High doses of folate can correct the megaloblastic anemia caused by B12 deficiency, masking the hematological signs while B12-dependent neurological damage continues unchecked. This is why folate and B12 should always be supplemented together, and B12 levels should be checked before starting high-dose folate.
What foods are highest in folate?
Chicken liver provides about 770 mcg per 3 oz serving. Lentils (358 mcg/cup cooked), spinach (263 mcg/cup cooked), asparagus (243 mcg/cup), and black-eyed peas (358 mcg/cup) are excellent plant sources. Fortified cereals and breads contribute significantly to population intake.
Does folate help with depression?
Low folate status is consistently associated with depression and poor antidepressant response. L-methylfolate (15 mg/day as Deplin) is FDA-approved as adjunctive therapy for depression when SSRIs alone are insufficient. Folate is required for SAMe production, which supports serotonin, dopamine, and norepinephrine synthesis.
References
- Prevention of neural tube defects: results of the Medical Research Council Vitamin Study. MRC Vitamin Study Research Group. The Lancet (1991)View study
- 5-Methyltetrahydrofolate increases plasma folate more effectively than folic acid in women with the MTHFR 677TT genotype. Prinz-Langenohl R, Brämswig S, Tober M, et al.. American Journal of Clinical Nutrition (2009)View study
- Homocysteine lowering and cardiovascular events after acute myocardial infarction (HOPE-2). Lonn E, Yusuf S, Arnold MJ, et al.. New England Journal of Medicine (2006)View study
- Overview of folate metabolism with implications for homocysteine and neural tube defects. Blom HJ, Smulders Y. Clinical Chemistry and Laboratory Medicine (2011)
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This entry is for educational purposes only. It is not medical advice. Always consult a qualified healthcare provider before starting, stopping, or changing any supplement regimen, especially if you take medications or have health conditions.