Recommended Daily Folic Acid Supplementation Dose
All women of childbearing age should take 400-800 μg (0.4-0.8 mg) of folic acid daily, regardless of pregnancy plans, through supplementation, fortified foods, or multivitamins. 1, 2, 3
Standard Dosing for General Population
For most women of reproductive age:
- 400-800 μg (0.4-0.8 mg) daily is the recommended dose endorsed by the US Preventive Services Task Force and American College of Medical Genetics 1, 2, 3
- This dose should be taken continuously throughout the reproductive years, not just when planning pregnancy, since approximately 50% of pregnancies are unplanned 2
- Supplementation should ideally begin at least 1 month before conception and continue through the first trimester for maximal neural tube defect prevention 2
- This dosing achieves a 40-80% reduction in neural tube defects depending on baseline prevalence 4
During pregnancy:
- Continue 400 μg (0.4 mg) daily throughout pregnancy as part of standard prenatal vitamins after the first trimester to support fetal growth and development 2
- For pregnant and lactating women, maintenance doses up to 800 μg (0.8 mg) are appropriate 5
High-Risk Population Dosing
Women at high risk require 4 mg (4000 μg) daily and include those with: 4, 1, 2
- Prior pregnancy affected by neural tube defect
- Personal history of neural tube defect
- First-degree relative with neural tube defect
- Type 1 diabetes mellitus
- Use of antiseizure medications (valproic acid, carbamazepine, phenytoin) 2, 6
High-risk dosing protocol:
- Begin 4 mg daily at least 1 month (preferably 3 months) before conception 4, 2
- Continue through 12 weeks gestation 1, 2
- After 12 weeks, reduce to standard 400 μg (0.4 mg) daily 1
- These women should receive genetic counseling before conception 4
Critical Safety Threshold
Total daily folic acid intake should not exceed 1000 μg (1 mg) unless prescribed by a physician 4, 2
Rationale for upper limit:
- Doses exceeding 1 mg daily may mask vitamin B12 deficiency, potentially allowing irreversible neurologic damage to progress undetected 4, 2
- However, this concern is primarily theoretical—vitamin B12 deficiency is rare in women of childbearing age, and recent evidence shows fortification has not led to increased masking of B12 deficiency 4
- Doses above 1 mg do not enhance hematologic effects, and excess is excreted unchanged in urine 4, 5
Important Clinical Considerations
Bioavailability differences:
- Synthetic folic acid in supplements is approximately twice as bioavailable as natural dietary folates 4, 6
- Food fortification alone (140 μg per 100g grain) provides insufficient protection, adding only ~100 μg daily 4, 7
- Average dietary folate intake is only ~230 μg daily, well below protective levels 6
Common pitfall to avoid:
- Do not wait until pregnancy is confirmed to start supplementation—neural tube closure occurs 23-27 days after conception, often before pregnancy recognition 4, 6
- The critical period is before most women know they are pregnant, making preconceptional supplementation essential 8
Limitations of supplementation: