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Vitamin B9 for stroke prevention

Goal: To lower the risk of a first stroke, as trials of folic acid in adults with high blood pressure tested it.

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

0.8 mg of folic acid a day with 10 mg of enalapril, a blood pressure medicine, in the China Stroke Primary Prevention Trial.[1] In a review of 21 trials, the effect did not depend on the dose.[2]

Form

Folic acid in one pill with enalapril.[1]

How long

A median of 4.5 years in the China Stroke Primary Prevention Trial.[1]

What studies found

A 2024 review of 21 trials with 115,559 people: 10% fewer strokes (risk ratio 0.90). In areas without folic acid in grain, or with only partly fortified grain, the risk ratio was 0.83, and in areas with fortified grain 1.04.[2] In a trial of 20,702 adults with high blood pressure in China, first strokes were 2.7% against 3.4% (hazard ratio 0.79).[1] A Cochrane review found no effect on heart attacks or deaths.[3]

Ask a doctor first

In countries that add folic acid to grain, such as the US, the benefit seems to be small or absent.[2][4] The US upper limit for adults is 1,000 µg of folic acid a day from supplements and fortified foods.[4] Folate interacts with methotrexate and medicines for epilepsy, and large amounts can hide a vitamin B12 deficiency.[4] Ask a doctor or pharmacist before starting if you take methotrexate, a medicine for epilepsy or sulfasalazine.[4]

References

  1. Efficacy of folic acid therapy in primary prevention of stroke among adults with hypertension in China: the CSPPT randomized clinical trial. Huo Y, Li J, Qin X, Huang Y, Wang X, Gottesman RF, et al. JAMA, 2015. PMID 25771069
  2. Folic acid supplementation for stroke prevention: A systematic review and meta-analysis of 21 randomized clinical trials worldwide. Zhang N, Zhou Z, Chi X, Fan F, Li S, Song Y, et al. Clin Nutr, 2024. PMID 38824900
  3. Homocysteine-lowering interventions for preventing cardiovascular events. Martí-Carvajal AJ, Solà I, Lathyris D, Dayer M Cochrane Database Syst Rev, 2017. PMID 28816346
  4. Folate: Fact Sheet for Health Professionals. NIH Office of Dietary Supplements. ods.od.nih.gov