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Evidence-Based Supplement Research
Evidence-Based Supplement Research
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Vitamin B9

What does the research say about Vitamin B9?

2 health outcomes synthesised

Vitamin B9 (folate) has been studied for 2 health outcomes. The strongest evidence, based on 6 studies, supports its role in reducing homocysteine levels, with effective doses ranging from 400 μg to 1 mg per day observed in diverse adult populations. Research also indicates moderate evidence for increasing folate levels, though the evidence base is smaller.

Strongest evidence: The highest-quality research on vitamin B9 focuses on reducing homocysteine levels. Across 6 studies (5 beneficial, 1 neutral), high evidence strength supports a beneficial effect, with doses of 400 μg to 1 mg per day over a median of 12 weeks. Effect sizes varied from small to large. Moderate evidence from 3 studies (2 beneficial with large effect sizes, 1 neutral) indicates that vitamin B9 supplementation increases folate levels, particularly at a dose of 1 mg per day.

Mixed or weaker evidence: No outcomes with low or very low evidence strength were identified in the available syntheses. However, one study in children with sickle cell disease found no significant effect on homocysteine, and a rice fortification trial showed a small neutral effect on folate levels, highlighting that benefits may not be universal.

Effective dose patterns: Both outcomes converge on a daily dose around 1 mg per day. For homocysteine reduction, doses from 400 μg to 1 mg were effective; for increasing folate levels, the only directly observed effective dose was 1 mg per day. The median study duration for both outcomes was 84 days (12 weeks), suggesting that short-term effects are typically observed within that timeframe.

Population insights: Studies included healthy adults, patients with coronary heart disease, individuals with type 2 diabetes, and those with phenylketonuria. The beneficial effects on homocysteine were seen across these diverse groups, but the single trial in children with sickle cell disease reported no effect, indicating potential population-specific limitations.

Notable caveats: Many studies used combined B-vitamin supplementation (e.g., B6, B12 with B9), making it difficult to isolate the effect of vitamin B9 alone. The evidence for increasing folate levels is based on only 3 studies and should be considered preliminary. Additionally, differences between folic acid and l-5-MTHF forms remain underexplored, and one beneficial trial used l-5-MTHF specifically, which may not be representative of all vitamin B9 forms.

Frequently asked

  • What is Vitamin B9 good for according to research?
    Research shows vitamin B9 supplementation is beneficial for reducing homocysteine levels (high evidence from 6 studies, 5 beneficial) and increasing folate levels (moderate evidence from 3 studies, 2 beneficial). These effects have been observed in diverse adult populations with doses ranging from 400 μg to 1 mg per day.
  • What dose of Vitamin B9 is typically used in studies?
    For reducing homocysteine, doses between 400 μg and 1 mg per day are most common. For increasing folate levels, the only directly studied dose in a beneficial trial was 1 mg per day. Both outcomes have a median study duration of 12 weeks.
  • Who benefits most from Vitamin B9?
    Studies show benefits in healthy adults, patients with coronary heart disease, those with type 2 diabetes, and individuals with phenylketonuria. However, one trial in children with sickle cell disease found no significant effect on homocysteine, suggesting the benefit may not apply to all populations.
  • Are there caveats or limitations in the research on Vitamin B9?
    Yes. Many studies combined vitamin B9 with other B vitamins, making it difficult to determine B9's independent effect. The evidence for increasing folate levels is based on only 3 studies and is considered preliminary. Differences between folic acid and l-5-MTHF forms are not well studied, and one beneficial trial used l-5-MTHF specifically.
  • Does Vitamin B9 help reduce homocysteine levels?
    Yes, high evidence from 6 studies (5 beneficial, 1 neutral) supports that vitamin B9 supplementation reduces homocysteine levels. Effect sizes ranged from small to large, and doses of 400 μg to 1 mg per day were effective in diverse adult populations over a median of 12 weeks.
  • Does Vitamin B9 increase folate levels?
    Moderate evidence from 3 studies suggests vitamin B9 supplementation increases folate levels, with two studies showing large beneficial effects. One study on rice fortification showed a small neutral effect. The beneficial trial used l-5-MTHF at 1 mg per day. The evidence base is small, so conclusions are preliminary.

Most-studied combinations with Vitamin B9

most supplement research is combination research
Also studied with:L-Methylfolate (3), Blood Orange (2), Zinc (2), Magnesium (2), Iron (3), Vitamin B2 (2), Vitamin B6 (3), Vitamin B12 (6), Vitamin D (3), Vitamin D3 (2)
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