tuneTypical Dose
400-800 mcg DFE
Vitamin
Vitamin B9
Pteroylglutamic acid (Folic acid) / 5-MTHF (Methylfolate)
Evidence TierAWADA NOT PROHIBITED
watchEffect Window
Must be taken prior to conception for NTD prevention. Allow 4-6 weeks for homocysteine.
check_circleCompliance
WADA NOT PROHIBITED
Overview
Clinical Summary
Vitamin B9 (folate) supports DNA synthesis and methylation. It is used to prevent neural tube defects when taken before conception and early pregnancy and to correct folate deficiency anemia.
Folate use before conception and in early pregnancy strongly reduces neural tube defect risk. It corrects folate deficiency anemia and lowers homocysteine levels. Minority evidence suggests adjunct benefit in depression in some individuals with low folate status. High folate intake can mask B12 deficiency, so benefit depends on ensuring both folate and B12 adequacy and avoiding unnecessary high dosing.
Coenzyme in single-carbon transfers essential for DNA/RNA synthesis, methylation cycle, and homocysteine metabolism.
Outcomes
What This Is Expected To Influence
Primary Outcomes
- Prevents neural tube defects
- Lowers homocysteine with B12/B6
Secondary Outcomes
- Adjunct therapy for SSRI-resistant depression (L-methylfolate form)
- Supports DNA synthesis and cell division
Safety
Contraindications and Interactions
Contraindications
- Undiagnosed B12 deficiency
Side effects
- GI upset at high folic acid doses (rare)
Interactions
- Methotrexate (folate antagonist)
- Phenytoin/carbamazepine (mutual interference)
Avoid if
- Methotrexate for cancer without oncologist guidance
- Unconfirmed B12 status at high doses
Evidence
Study-level References
vitamin-b9-SRC-001Randomized controlled trial
Sourceopen_in_newMRC Vitamin Study Research Group. "Prevention of neural tube defects: results of the Medical Research Council Vitamin Study." Lancet. 1991.
Population: Women with prior NTD-affected pregnancy
Key findings: Folic acid supplementation reduced NTD recurrence by 72%, establishing the foundation for universal preconception folate recommendations.
Paper content
Folic acid supplementation reduced NTD recurrence by 72%, establishing the foundation for universal preconception folate recommendations.
vitamin-b9-SRC-002Meta-analysis of randomized controlled trials
Sourceopen_in_newHomocysteine Lowering Trialists' Collaboration. "Dose-dependent effects of folic acid on blood concentrations of homocysteine." Am J Clin Nutr. 2005.
Population: Adults with varying baseline homocysteine
Key findings: Folic acid reliably lowers homocysteine in a dose-dependent manner. Adding B12 provides additional benefit.
Paper content
Folic acid reliably lowers homocysteine in a dose-dependent manner; adding B12 provides additional benefit.
vitamin-b9-SRC-003Randomized controlled trial
Sourceopen_in_newPapakostas GI, Shelton RC, Zajecka JM, et al. "L-methylfolate as adjunctive therapy for SSRI-resistant major depression." Am J Psychiatry. 2012.
Population: Adults with major depressive disorder inadequately responding to SSRIs
Key findings: L-methylfolate 15 mg/day as adjunct to SSRI showed significant improvement vs placebo. Benefit appeared stronger in patients with markers of impaired methylation.
Paper content
L-methylfolate 15 mg/day as adjunct to SSRI showed significant improvement vs placebo; benefit appeared stronger in patients with markers of impaired methylation.
vitamin-b9-SRC-004Systematic review and meta-analysis of randomized controlled trials.
Sourceopen_in_newRen R, Yang A, Chow A, et al. Complex effects of B-vitamin combinations on cardiovascular diseases: a systematic review and meta-analysis of randomized controlled trials over three decades. Nutrients. 2026;18(5):842. doi:10.3390/nu18050842. PMID:41830012.
Population: Participants across 13 randomized trials totaling 68,363 individuals.
Dose protocol: B-vitamin combinations including folate across 13 RCTs with 68,363 participants
Key findings: Nonsignificant stroke reduction overall, but meaningful reductions in primary prevention populations. No significant MI or mortality benefit.
Notes: Adds nuance to folate cardiovascular story by distinguishing primary from secondary prevention and noting that regional fortification modulates treatment effects.
Paper content
This large meta-analysis pooled 13 RCTs with 68,363 participants to assess the cardiovascular effects of B-vitamin combination supplementation over three decades. Overall, B-vitamin combinations showed a nonsignificant reduction in stroke. However, in primary prevention populations, the signal for stroke and major adverse cardiovascular events was more meaningful, while secondary prevention results were more modest. No significant effects were found for myocardial infarction or mortality. The authors noted that baseline cardiovascular risk and regional folic acid fortification status influence the treatment effect. This study is relevant to folate (B9) as a key component of the B-vitamin combinations tested, and it nuances the cardiovascular story by distinguishing primary from secondary prevention settings.
vitamin-b9-SRC-005Cross-sectional dose-response analysis.
Sourceopen_in_newZeng W, Ma H, Wei S, et al. Red blood cell folate and depression risk in U.S. women: a dose-response analysis from a nationwide cross-sectional study (2009-2018). Medicine (Baltimore). 2026. doi:10.1097/MD.0000000000048023. PMID:41824854.
Population: 9,409 U.S. women from NHANES 2009 to 2018.
Dose protocol: Observational RBC folate dose-response analysis in 9,409 U.S. women from NHANES 2009 to 2018
Key findings: U-shaped relationship with depression risk. Below 985 nmol/L, each 100 nmol/L increase in RBC folate reduced depression risk by 6%. Above this level, risk increased by 3% per 100 nmol/L.
Notes: Cross-sectional design. Supports adequate but not excessive folate for mental health. Identifies potential upper-bound concern.
Paper content
This cross-sectional analysis of 9,409 U.S. women from NHANES (2009 to 2018) found a U-shaped relationship between red blood cell folate and depression risk. Below a threshold of 985 nmol/L, each 100 nmol/L increase in RBC folate was associated with a 6% lower depression risk. Above this threshold, additional folate was associated with a 3% increase in depression risk per 100 nmol/L. Both the lowest and highest folate quartiles showed elevated depression odds compared to mid-range levels. This supports the concept that maintaining adequate but not excessive folate levels is optimal for mental health, and it adds nuance to the folate-depression relationship by identifying a potential upper-bound concern.