Vitamin B9

How long does folic acid take to raise folate levels?

Updated 9 Nov 2026

Short answer

Weeks to months. In a 24-week trial in 144 young women, folate in plasma, the liquid part of the blood, stopped rising after 12 weeks. Folate in red blood cells was still rising at 24 weeks.[1] A calculation from two trials in young women puts the time to a stable red blood cell level at about 40 weeks.[2] The authors suggest starting more than 4 weeks before pregnancy.[1]

Sources (2)

  1. Red blood cell folate concentrations increase more after supplementation with [6S]-5-methyltetrahydrofolate than with folic acid in women of childbearing age. Lamers Y, Prinz-Langenohl R, Brämswig S, Pietrzik K Am J Clin Nutr, 2006. PMID 16825690
  2. Calculation of red blood cell folate steady state conditions and elimination kinetics after daily supplementation with various folate forms and doses in women of childbearing age. Pietrzik K, Lamers Y, Brämswig S, Prinz-Langenohl R Am J Clin Nutr, 2007. PMID 17991654

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For education; not medical advice. Talk to a doctor before you start, stop or change a supplement.