Researchers reviewed dozens of studies involving millions of families to understand whether taking folic acid and multivitamins during pregnancy affects autism risk in children. They found that mothers who took these supplements during pregnancy had children with about 30% lower risk of autism spectrum disorder. Multivitamins showed slightly stronger protection at 34% risk reduction. While these findings are encouraging and suggest prenatal vitamins may have protective benefits, experts emphasize that autism has many causes and supplements are just one piece of a complex puzzle. This research could help guide public health recommendations for pregnant women.

The Quick Take

  • What they studied: Whether taking folic acid and multivitamin supplements during pregnancy reduces the chances of a child developing autism spectrum disorder
  • Who participated: Analysis of 101 previous research studies involving over 3 million pregnant women and their children from around the world
  • Key finding: Mothers who took folic acid or multivitamins during pregnancy had children with approximately 30% lower risk of autism, with multivitamins showing slightly stronger protection at 34% lower risk
  • What it means for you: If you’re planning pregnancy or currently pregnant, taking prenatal vitamins containing folic acid may help reduce autism risk in your child. However, this doesn’t guarantee autism won’t occur, as many factors influence autism development. Talk with your doctor about prenatal supplementation as part of your overall pregnancy care.

The Research Details

This was an umbrella review, which means researchers looked at existing systematic reviews and meta-analyses rather than conducting new experiments. They searched four major scientific databases for all relevant studies published up to their review date. They included 8 high-quality systematic reviews that had already analyzed 101 individual research studies. The researchers used strict quality standards to evaluate each review using a tool called AMSTAR, which checks for potential bias and methodological problems. They then combined the results from all these studies using statistical methods to get an overall picture of the relationship between prenatal vitamins and autism risk.

The researchers were careful to look at different types of supplements separately—folic acid alone versus multivitamins—to see if one was more protective than the other. They also checked whether results differed based on study location, population characteristics, and other factors. They assessed whether the studies agreed with each other and looked for signs of publication bias, which occurs when only positive results get published.

This approach is powerful because it combines evidence from millions of people across many studies, giving us a much clearer picture than any single study could provide. By reviewing existing high-quality reviews rather than individual studies, the researchers could synthesize the strongest available evidence efficiently. This type of analysis helps doctors and public health officials make recommendations based on the best available science.

The study included only high-quality systematic reviews that had already been peer-reviewed, which strengthens confidence in the findings. The researchers used rigorous statistical methods and assessed the certainty of evidence using GRADE criteria, which rates how confident we can be in results. The large sample size (over 3 million participants) and consistency of findings across multiple studies increases reliability. However, the quality depends on the original studies included, and some variation existed between studies.

What the Results Show

The main finding was that prenatal folic acid and multivitamin supplementation together were associated with a 30% reduction in autism risk in children. This means that if autism occurred in 100 children whose mothers didn’t take supplements, it might occur in only 70 children whose mothers did take supplements. When researchers looked at multivitamins separately, the protection was slightly stronger at 34% risk reduction. Folic acid alone showed a 30% reduction in risk.

These associations were consistent across the studies reviewed, meaning different research groups in different countries found similar results. The researchers rated this evidence as “highly suggestive,” which is a high level of confidence in scientific terms. The findings held up even when researchers performed additional analyses to check if results were influenced by how studies were conducted or reported.

When researchers examined different groups of people, the protective effect appeared consistent across various populations and study designs. The findings were robust, meaning they didn’t change significantly when researchers removed individual studies or adjusted their analysis methods. No strong evidence of publication bias was detected, suggesting that negative studies weren’t being hidden from the scientific record.

Previous individual studies on this topic had shown mixed results, with some suggesting protection and others finding no clear relationship. This umbrella review brings clarity by combining all available evidence, showing that when you look at the big picture across millions of people, a protective effect does appear. The findings align with biological understanding that folic acid and B vitamins play important roles in fetal brain development.

The study cannot prove that supplements directly cause the reduced autism risk—only that they’re associated with it. Other factors that differ between mothers who take supplements and those who don’t (like overall health awareness or prenatal care access) might explain some of the difference. The original studies varied in how they measured autism and supplement use, which could affect results. The research is observational rather than experimental, meaning researchers watched what happened naturally rather than randomly assigning some women to take supplements and others not to. Additionally, autism has many causes, and supplements represent just one potential factor among many genetic and environmental influences.

The Bottom Line

If you are pregnant or planning pregnancy, discuss prenatal vitamin supplementation with your healthcare provider. Current evidence suggests taking folic acid and multivitamins during pregnancy may help reduce autism risk in your child (confidence level: high). Prenatal vitamins offer other well-established benefits for fetal development, including reduced risk of neural tube defects. However, supplements should complement, not replace, other important prenatal care like regular checkups and healthy lifestyle choices.

This research is most relevant for pregnant women and those planning pregnancy. It’s also important for healthcare providers, public health officials, and policymakers considering prenatal health recommendations. Women with specific health conditions or medication interactions should consult their doctor before starting supplements. This research doesn’t apply to people who already have autism—supplements won’t change an autism diagnosis.

Prenatal supplementation would need to occur during pregnancy to potentially have protective effects, as the critical period for fetal brain development is during gestation. You wouldn’t expect to see effects after a child is born. If you start supplements when planning pregnancy, aim to begin at least one month before conception, as folic acid builds up in your system over time.

Want to Apply This Research?

  • If using a pregnancy or health app, track daily prenatal vitamin intake by logging supplement type, dosage, and whether you took it each day. Record the specific folic acid and multivitamin brands used, as this helps you maintain consistency and provides information for your healthcare provider.
  • Set a daily reminder on your phone or app to take prenatal vitamins at the same time each day (such as with breakfast). Use the app to track streaks of consistent supplement use, celebrating weekly milestones to build the habit. Share your supplement tracking with your healthcare provider during prenatal visits.
  • Use your app to maintain a record of prenatal supplement use throughout pregnancy and share monthly summaries with your healthcare provider. Track any side effects or concerns with supplements. After pregnancy, keep records of what you took during each trimester, as this information may be relevant for your child’s health history and future medical care.

This research suggests an association between prenatal vitamin supplementation and reduced autism risk, but cannot prove causation. Autism spectrum disorder is a complex condition with multiple genetic and environmental factors. Taking prenatal vitamins is not a guarantee against autism and should not replace other important prenatal care. Always consult with your healthcare provider before starting any supplement regimen during pregnancy or when planning pregnancy. This information is for educational purposes and should not be considered medical advice. Individual circumstances vary, and your doctor can provide personalized recommendations based on your health history and needs.