Vitamin B9

vitamin

Best with a mealTake with food

What is it

Vitamin B9 is the collective name for folate (the natural form in food) and folic acid (the synthetic form in supplements and fortified foods). It is essential for DNA synthesis, cell division, and red blood cell formation.

How it works

B9 is a cofactor in one-carbon metabolism, which provides the methyl groups needed to build DNA and the bases that form it. It is critical during rapid cell division, which is why deficiency causes megaloblastic anemia (large, immature red blood cells) and increases the risk of neural tube defects in early pregnancy. All B9 forms are eventually converted to 5-methyltetrahydrofolate, the active circulating form. The body uses methyl-folate alongside vitamin B12 to convert homocysteine to methionine, supporting methylation reactions throughout the body.

Evidence for 5 uses

AI-assisted evidence assessment — talk to your doctor before relying on any single supplement.

Prevention of neural tube defects

Grade A

Strong evidence

Folic acid supplementation around conception substantially reduces neural tube defects like spina bifida. One of the most well-established preventive interventions in nutrition.

Treatment of megaloblastic anemia

Grade A

Strong evidence

B9 supplementation reverses folate-deficiency anemia. Standard treatment for the deficiency.

Lowering homocysteine

Grade A

Strong evidence

B9 with B12 and B6 reliably lowers blood homocysteine. Whether this prevents cardiovascular events is uncertain — large trials have mostly not shown benefit.

Depression adjunct

Grade C

Moderate evidence

Some trials suggest L-methylfolate as an add-on to antidepressants may improve response, particularly in people with low folate or MTHFR variants. Evidence is limited and mixed.

Cancer prevention

Grade D

Mixed evidence

Observational links between folate intake and lower cancer risk; supplement trials have shown mixed results, with some suggesting harm at high doses in people with established colorectal lesions.

3 commercial forms

Folic acid

synthetic, very stable, high bioavailability

The form used in fortified foods and most supplements. Inexpensive and effective for raising folate status and preventing neural tube defects.

Folate (food folate)

natural, less stable

Found in leafy greens, legumes, and other foods. About 50 percent bioavailable compared to folic acid; cooking reduces content.

L-5-Methyltetrahydrofolate (5-MTHF, methylfolate)

active form, bypasses MTHFR step

The biologically active form. Useful for people with MTHFR genetic variants and avoids potential issues with unmetabolized folic acid. More expensive.

Dosage

The RDA is 400 mcg of dietary folate equivalents (DFE) per day for adults. Pregnant women need 600 mcg and breastfeeding women 500 mcg. Women planning pregnancy are advised to start 400 mcg of folic acid daily at least one month before conception to reduce neural tube defect risk. The tolerable upper limit for folic acid from supplements and fortified foods is 1,000 mcg per day for adults.

When and how to take it

B9 absorbs well with or without food. Daily dosing is standard. Pregnant women and those planning pregnancy should take their dose consistently every day — the protective effect against neural tube defects requires adequate levels at the time the neural tube closes, early in the first trimester.

Food sources

Food	Amount	%DV
Beef liver, 3 oz cooked	215 mcg DFE	54%
Spinach (boiled), 1/2 cup	131 mcg DFE	33%
Lentils (boiled), 1/2 cup	179 mcg DFE	45%
Chickpeas (canned), 1/2 cup	141 mcg DFE	35%
Asparagus (boiled), 1/2 cup	134 mcg DFE	34%
Avocado, 1/2 cup	59 mcg DFE	15%
Fortified breakfast cereal	100 to 400 mcg DFE	25%
Enriched pasta, 1 cup cooked	153 mcg DFE	38%

Safety

B9 from food is safe at any intake level. The 1,000 mcg upper limit for folic acid is meant to prevent masking of vitamin B12 deficiency — folic acid can correct B12-deficiency anemia without correcting the underlying neurological damage, allowing nerve injury to progress unnoticed. Always check B12 status if taking high-dose folic acid long-term.

Who should be cautious

Pregnant women and women planning pregnancy should ensure adequate B9 intake. Older adults at risk of B12 deficiency should not take high-dose folic acid without confirming B12 status. People with MTHFR genetic variants are sometimes advised to take 5-MTHF (methylfolate) instead of folic acid, though clinical importance is debated.

Interactions

Methotrexate (used for cancer and autoimmune disease) deliberately blocks folate metabolism — supplementation is often co-prescribed in lower-dose autoimmune use but must be coordinated with the prescriber. Anticonvulsants like phenytoin and phenobarbital reduce folate levels. Some antibiotics (trimethoprim, sulfasalazine) interfere with folate absorption or metabolism.

Frequently asked questions

What is the difference between folate and folic acid?⌄

Folate is the natural form in food. Folic acid is the synthetic form used in supplements and fortified foods. Both are converted to active 5-MTHF in the body.

When should I start taking folic acid for pregnancy?⌄

At least one month before conception. The neural tube closes very early — often before a woman knows she is pregnant — so folate must already be adequate.

Is methylfolate worth the extra cost?⌄

For most people, folic acid works fine. Methylfolate may be preferable for those with MTHFR variants or who prefer to avoid unmetabolized folic acid.

Can too much folic acid be harmful?⌄

High doses can mask B12 deficiency, allowing nerve damage to progress undetected. The upper limit from supplements and fortified foods is 1,000 mcg per day.

Does folic acid affect cancer risk?⌄

The data is mixed. Adequate intake supports DNA stability, but very high doses have been associated with increased cancer growth in people with pre-existing lesions. Stick to the RDA unless your doctor advises otherwise.

Track Vitamin B9 with Pilora

Set up dose reminders, check interactions, and join the community in the Pilora iPhone app.

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Disclaimer: These statements have not been evaluated by the FDA. This page is educational, not a substitute for personalized medical advice. Evidence grades are AI-assisted assessments — talk to your doctor before starting any new supplement, especially if you're pregnant, breastfeeding, on medications, or managing a chronic condition.