Folic acid is an essential vitamin that is important for many bodily functions, including DNA synthesis and repair. It is especially critical for pregnant women to get adequate folic acid to reduce the risk of neural tube defects in the developing baby. However, some researchers have raised concerns that getting too much folic acid, especially during pregnancy, could increase the risk of autism in children. This article will examine the evidence surrounding this controversial hypothesis.
What is folic acid?
Folic acid, also known as vitamin B9 or folate, is a B vitamin that is naturally found in foods such as dark green leafy vegetables, citrus fruits, beans, peas, and lentils. It is essential for many bodily functions including:
- DNA synthesis and repair
- Cell division and growth
- Production of red blood cells
- Cognitive function and mental health
Folic acid works closely with vitamin B12 and vitamin C to perform these critical functions. A deficiency in folic acid can lead to anemia and elevated homocysteine levels, which increases heart disease risk.
During pregnancy, adequate folic acid is crucial to proper fetal development. Taking folic acid supplements before and during early pregnancy can significantly reduce the risk of neural tube defects like spina bifida. Neural tube defects are birth defects of the brain, spine or spinal cord that occur within the first few weeks of pregnancy, often before a woman knows she is pregnant.
Folic acid supplementation recommendations
Because folic acid needs increase during pregnancy, public health authorities like the CDC recommend the following daily intake:
- Non-pregnant women: 400 micrograms (mcg)
- Pregnant women: 600 mcg
- Breastfeeding women: 500 mcg
Many countries fortify cereals and grains with folic acid to help people get adequate intake. Still, it is difficult to get enough folic acid from diet alone, so supplements are often recommended for pregnant women and women trying to conceive.
Too much folic acid and autism concerns
Although folic acid is clearly beneficial in preventing birth defects, some researchers have raised concerns that getting excessive folic acid, especially during pregnancy, could increase the risk of autism spectrum disorder (ASD) in children.
The hypothesis is that too much folic acid during critical windows of fetal brain development could disrupt normal processes and increase susceptibility to developmental disorders like autism. This is still a theoretical concern based on limited research, but it has gained attention in recent years.
Key studies on high folic acid intake and autism
Some of the key studies linking high maternal folic acid intake to increased autism risk include:
- A 2015 study from Johns Hopkins University found that mothers who took very high levels of folic acid supplements (over 800 mcg) were more than twice as likely to have a child with autism compared to mothers who took no supplements.
- A Norwegian study published in 2013 found that mothers who took folic acid supplements in pregnancy had a higher risk of giving birth to children who later developed autism, especially when supplements were taken 8 weeks after conception.
- A 2011 California study found that mothers of autistic children were significantly more likely to have taken prenatal vitamins during the 3 months before pregnancy and the first month of pregnancy.
However, these studies do not prove cause-and-effect and have significant limitations. Many other factors besides folic acid intake could account for the differences observed.
Proposed mechanisms
Researchers have proposed a few biological mechanisms to explain how excess folic acid might contribute to autism risk:
- Masking vitamin B12 deficiency: High folic acid intake can mask an underlying vitamin B12 deficiency. B12 deficiency during pregnancy may increase oxidative stress and epigenetic changes in the fetal brain that disrupt normal development.
- Abnormal DNA methylation: Excess folic acid could disturb normal DNA methylation patterns in the developing fetal brain. Altered DNA methylation could affect gene expression and neural development.
- Reduced natural killer cell activity: High levels of unmetabolized folic acid in the blood is linked to decreased natural killer cell cytotoxicity. This may reduce defenses against infections or toxins during pregnancy that could impact fetal neurodevelopment.
However, these mechanisms are speculative and not well proven. More research is needed to understand if and how folic acid supplementation at varying dosages might alter fetal brain development.
Folic acid benefits likely outweigh unproven risks
Despite theoretical concerns, major health and pediatric organizations agree the proven benefits of folic acid supplementation during pregnancy still far outweigh any unproven risks.
Reasons to continue recommending folic acid supplementation include:
- Prevents neural tube defects: Folic acid supplementation reduces neural tube defect risk by up to 70%.
- May lower autism risk in some cases: Getting adequate folic acid helps proper fetal brain development, which could potentially lower autism risk in some cases.
- Limited evidence of harm: Evidence linking folic acid intake to autism is circumstantial and inconclusive. It is based on observational studies that cannot prove cause-and-effect.
- Difficult to isolate effect of folic acid: Autism likely has many contributing factors. Isolating the effect of one nutrient like folic acid is extremely difficult.
- Benefits clearly demonstrated: The evidence of benefits from folic acid is concrete, while evidence of risk is theoretical.
- Preconception supplementation important: By the time most women know they are pregnant, the critical time for neural tube defect prevention has already passed.
Current folic acid recommendations
Based on the evidence, health authorities continue to recommend the following:
- Women take 400 mcg of folic acid daily before pregnancy and 600 mcg daily during pregnancy to prevent neural tube defects.
- Folic acid from supplements or fortified foods should not exceed 1,000 mcg per day, even during pregnancy.
- Folic acid supplements are most critical during the time immediately before and shortly after conception.
- Women should focus on getting folic acid from a balanced diet of folate-rich whole foods.
- Folic acid supplements should not be excessive or taken for long periods of time outside of pregnancy.
Dietary sources of folate
The best way to meet daily folate needs is to eat a varied diet with plenty of folate-rich foods, including:
- Leafy green vegetables: spinach, asparagus, broccoli, lettuce
- Fruits: citrus fruits, bananas, melons
- Legumes: beans, peas, lentils
- Nuts and seeds: peanuts, sunflower seeds, almonds
- Grains: whole wheat bread, rice, pasta
- Dairy: milk, yogurt
- Meat and eggs
- Seafood: salmon, tuna
Eating these folate-containing foods ensures you get the vitamin from natural food sources along with other nutrients. However, research shows many women still fall short of getting sufficient folate from diet alone.
| Food | Serving | Folate (mcg) |
|---|---|---|
| Spinach | 1⁄2 cup | 58 |
| Asparagus | 4 spears | 64 |
| Broccoli | 1⁄2 cup | 44 |
| Oranges | 1 orange | 38 |
| Beans | 1⁄2 cup | 127 |
| Fortified cereal | 3⁄4 cup | 400 |
Safety of folic acid supplements
Folic acid from supplements and fortified foods is more bioavailable than natural folate from foods. At low to moderate dosages, folic acid supplements are considered safe for women trying to conceive and during pregnancy.
However, extremely high dosages of folic acid from supplements may have some risks, including:
- Masking B12 deficiency symptoms
- Seizures at doses >5,000 mcg/day
- Impaired zinc and vitamin B12 absorption
- Other unexpected effects on health if taken long-term outside of pregnancy
That’s why the tolerable upper intake level for folic acid is set at 1,000 mcg/day for adults. Supplements should not exceed this dosage. Food sources do not pose a toxicity risk.
Autism risk factors
While the role of excess folic acid is debatable, research has identified other more convincing factors that increase autism risk, including:
- Advanced parental age: Children born to older parents are at higher risk.
- Preterm birth: Autism risk increases significantly with early delivery before 37 weeks.
- Preeclampsia: Women with this pregnancy complication are more likely to have autistic children.
- Birth spacing: Short intervals between pregnancies (<12 months) increase autism risk.
- SSRIs: Some studies link prenatal use of these antidepressants to increased autism risk.
- Genetics: Autism has a strong hereditary component.
The causes of autism are complex. Looking at the whole diet pattern and overall maternal health provides clearer insight compared to isolated nutrients like folic acid.
Conclusion
Current evidence indicates the benefits of folic acid supplementation for preventing neural tube defects far outweigh any potential relationship with autism, which remains theoretical.
Mothers should continue taking the recommended 400-600 mcg of folic acid daily when trying to conceive and during pregnancy to support fetal health. Aim to get the rest of your folate needs from whole food sources like leafy greens, beans, citrus fruits, nuts and seeds.
As with any nutrient, excessive folic acid intake from supplements can have risks. But at the standard supplemental dosages, folic acid is considered safe and essential for maternal and fetal health.
