Protocols › Vitamin B9

Vitamin B9 to prevent neural tube defects

Goal: To lower the risk of spina bifida and other neural tube defects, with folic acid before and in early pregnancy.

Each protocol describes what studies used, for one goal or for one group of people. It is not advice for you: talk to a doctor before you start a supplement.

Updated 9 Nov 2026
Dose

400 to 800 µg of folic acid a day, as recommended by the US Preventive Services Task Force.[1] WHO recommends 400 µg a day.[2] In the Cochrane review, the effect did not differ between 400 µg and higher doses.[3]

Form

Folic acid alone or in a multivitamin. The Hungarian trial used a multivitamin with 0.8 mg of folic acid.[4][3]

When to take

From the moment a woman starts trying to conceive until 12 weeks of pregnancy (WHO).[2]

How long

In the Hungarian trial, from at least 1 month before conception until the second missed period or later.[4]

What studies found

A 2015 Cochrane review of 5 trials with 7,391 women: risk ratio 0.31 for a neural tube defect, from 6,708 births, high-quality evidence. For women with an affected pregnancy before, risk ratio 0.34.[3] In the MRC trial of 1,817 such women, folic acid prevented 72% of neural tube defects.[5]

Ask a doctor first

After a pregnancy with a neural tube defect, WHO says women should be offered 5 mg a day.[2] Doses this high are above the upper limit of 1,000 µg a day and are taken only under medical care.[6] Medicines for epilepsy lower folate, and folate may lower their level.[6] Large amounts of folate can hide a vitamin B12 deficiency.[6] Ask a doctor or pharmacist before starting if you take methotrexate, a medicine for epilepsy or sulfasalazine, or had an affected pregnancy.[6]

References

  1. Folic Acid Supplementation to Prevent Neural Tube Defects: US Preventive Services Task Force Reaffirmation Recommendation Statement. Barry MJ, Nicholson WK, Silverstein M, Chelmow D, Coker TR, Davis EM, et al. JAMA, 2023. PMID 37526713
  2. Periconceptional folic acid supplementation to prevent neural tube defects. World Health Organization, 2023. www.who.int
  3. Effects and safety of periconceptional oral folate supplementation for preventing birth defects. De-Regil LM, Peña-Rosas JP, Fernández-Gaxiola AC, Rayco-Solon P Cochrane Database Syst Rev, 2015. PMID 26662928
  4. Prevention of the first occurrence of neural-tube defects by periconceptional vitamin supplementation. Czeizel AE, Dudás I N Engl J Med, 1992. PMID 1307234
  5. Prevention of neural tube defects: results of the Medical Research Council Vitamin Study. MRC Vitamin Study Research Group. Lancet, 1991. PMID 1677062
  6. Folate: Fact Sheet for Health Professionals. NIH Office of Dietary Supplements. ods.od.nih.gov