Folate (Vitamin B9)
B VitaminEssential B vitamin for DNA synthesis, methylation, and fetal development. The active form methylfolate is preferred over folic acid for those with MTHFR variants.
Evidence comparisons not yet run for these claims.
Expert Consensus
Evidence Summary
Folate (Vitamin B9) has been studied across a wide range of health conditions, and the existing body of research — spanning meta-analyses, systematic reviews, and randomized controlled trials — suggests it plays meaningful roles in pregnancy health, cardiovascular function, cognitive aging, and mental health. The evidence is particularly well-established for pregnancy supplementation, where systematic reviews support its role in reducing neural tube defects and supporting maternal B-vitamin status. Beyond pregnancy, research has examined folate's potential relevance to type 2 diabetes, breast cancer risk, schizophrenia, age-related macular degeneration, and osteoarthritis, among other conditions.
Read full evidence summary →Top studies
B vitamins and prevention of cognitive decline and incident dementia: a systematic review and meta-analysis.
B vitamins and prevention of cognitive decline and incident dementia: a systematic review and meta-analysis.
Folic acid supplementation on inflammation and homocysteine in type 2 diabetes mellitus: systematic review and meta-analysis of randomized controlled trials.
Folic acid supplementation on inflammation and homocysteine in type 2 diabetes mellitus: systematic review and meta-analysis of randomized controlled trials.
Expert Mentions
All 20 mentions
“first things to worry about if you're just focusing on plants only is a deficiency in folic acid.”
A deficiency in folic acid is one of the first things to worry about if you are eating a plant-based diet.
“he had found some humans um that were low and folate and did some experiments as well found a similar thing gave them back the folate DNA double stranded brakes went away”
In human subjects who were low in folate, DNA double-stranded breaks were observed, and restoring folate caused those breaks to go away.
Safety, interactions & who should avoid Folate (Vitamin B9)
Folate is generally considered safe at recommended dietary and supplemental doses, particularly in pregnant populations where it is widely endorsed. High-dose supplementation warrants caution, as excess folic acid may mask vitamin B12 deficiency and has been discussed in relation to cancer risk modification, though no definitive harm has been established in the reviewed literature.
Pregnancy & breastfeeding
Our sources specifically flag pregnancy or breastfeeding considerations for Folate (Vitamin B9) — see the cautions above.
We don’t assign pregnancy-safety ratings. Many supplements lack adequate safety data in pregnancy and breastfeeding, and the absence of a warning here does not mean a supplement is safe to take. Don’t start, stop, or continue any supplement while pregnant or nursing without your OB-GYN or midwife.
Read: Supplements during pregnancy & breastfeeding →This is educational information only. Consult a healthcare provider before starting any supplement.
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Key findings
- ·Systematic reviews and clinical trials consistently support folate supplementation during pregnancy for improving maternal B-vitamin status and reducing risk of neural tube defects.
- ·Meta-analyses suggest lower folate levels are associated with schizophrenia, and that folate may play a role in mental health outcomes, though causality is not fully established.
- ·Folic acid supplementation in type 2 diabetes has been studied for its effects on inflammation and homocysteine levels, with meta-analytic evidence suggesting potential benefit in these biomarkers.
Evidence gaps
- ·Many of the included studies lack reported sample sizes and specific population details, making it difficult to assess generalizability or statistical power across the evidence base.
- ·The distinction between folic acid (synthetic) and 5-methyltetrahydrofolate (the natural form) as supplements is underexplored in most studies, and it remains unclear whether the two forms differ meaningfully in clinical outcomes for various populations.
- ·Long-term safety and efficacy data for folate supplementation outside of pregnancy — particularly for conditions like cognitive decline, cancer risk modification, and mental health — are limited and largely derived from observational or secondary analyses rather than dedicated long-term RCTs.