Strong evidence13 studies

How we rate

“Strong” = several concordant meta-analyses or systematic reviews. “Moderate” = one synthesis, or several controlled trials. “Limited” = early trials only. The rating is about the quality of the studies, not about how useful the supplement is.

Folate (vitamin B9)

The pregnancy vitamin: before conception, it prevents neural tube defects. Outside of this context, large trials are more mixed.

Benefits

Taken before and at the very beginning of pregnancy, prevents neural tube defects: −72 % in 1,817 women who had already had an affected pregnancy, and zero cases compared to six in the control group in 4,753 women planning a pregnancy (multivitamin supplement with 0.8 mg of folic acid)
In over 20,000 hypertensive adults, 0.8 mg per day added to their treatment reduced the risk of first stroke by 21 %; across 30 trials and over 82,000 participants, a meta-analysis finds 10 % fewer strokes, especially in people with low folate levels or without cardiovascular disease
In 818 older adults, 800 µg per day for 3 years improved memory and information processing speed compared to placebo, with a 26 % drop in homocysteine

Precautions

On cancer, meta-analyses contradict each other: one (10 trials) finds a borderline significant increase in all cancers combined (+7 %) and a significant increase in prostate cancer (+24 %); another, on nearly 50,000 participants from 13 trials followed for an average of 5.2 years, finds no effect, neither overall nor by organ (colon, prostate, lung, breast). Finally, the limitations: in people who already have vascular disease, a meta-analysis on nearly 17,000 participants finds no reduction in cardiovascular disease, stroke, or mortality; the benefit on stroke is concentrated in people with low folate levels. On memory, a meta-analysis of 9 trials (2,835 participants) finds no effect within three years: the positive 3-year trial remains isolated. And the effect on the neural tube assumes starting before pregnancy.

Recommended dosage

0.4 to 0.8 mg (400 to 800 µg) of folic acid per day for any woman planning or able to start a pregnancy, according to the recommendation of the US Preventive Services Task Force (USPSTF). Start before conception: it is before and at the very beginning of pregnancy that trials measured the effect. Trials on stroke and memory used 0.8 mg per day.

Did you know?

Folic acid supplementation has not been proven effective in reducing the risk of cardiovascular disease or mortality in people with a prior vascular history.

What the studies say

This meta-analysis of 30 randomized clinical trials, involving over 82,000 participants, examined the effect of folic acid supplementation on the risk of cardiovascular disease. The results indicated a 10% reduction in stroke risk and a 4% reduction in the overall risk of cardiovascular disease with folic acid supplementation. Benefits were more pronounced in participants with low plasma folate levels or without pre-existing cardiovascular disease.
Li Y, Huang T, Zheng Y, Muka T, Troup J, Hu FB. — Journal of the American Heart Association (2016) — View the source study

Pairs well with

Myo-inositolTrials on gestational diabetes provide myo-inositol with folic acid: in pregnant women with a family history of diabetes, 2 g of myo-inositol twice a day with folic acid reduced gestational diabetes to 6% compared to 15.3% with the placebo. The measured effect is that of myo-inositol; folic acid, on the other hand, is what pregnancy already requires.

For information only: not a substitute for medical advice. Dietary supplements are not a replacement for a varied, balanced diet. Learn more