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Could folic acid help prevent autism?

Children born to women who take folic acid supplements before and during pregnancy are less likely to develop autism, a study shows. But we can’t yet be certain that folic acid was what reduced their risk.

BMJ Group News

What do we know already?


Folic acid plays an important role in pregnancy, with women advised to take 400 micrograms of this nutrient a day while they are trying to conceive and during their first 12 weeks of pregnancy. This is to help prevent birth defects called neural tube defects. One of the most common types is spina bifida, where the baby’s spine does not develop normally.

Some studies have suggested that folic acid may also play a role in preventing autism and related conditions, which together are called autism spectrum disorders (ASDs). Children with these disorders often have problems with learning and development, difficulty in communicating with and relating to other people, and repetitive behaviours. Autism is the most severe type of ASD.

In the new study, researchers looked at more than 85,000 children born in Norway from 2002 to 2008. Their mothers had filled in detailed questionnaires about their use of dietary supplements, including folic acid, before and after they became pregnant. The researchers then looked at whether children born to women who took folic acid were more or less likely to develop an ASD, compared with children born to women who did not take these supplements. The researchers looked separately at three types of ASDs: autism, Asperger’s syndrome, and a type called ‘pervasive developmental disorder - not otherwise specified’ (or PDD-NOS).

What does the new study say?

The researchers found that autism was less common among children born to women who’d taken folic acid for four weeks before becoming pregnant and eight weeks after. In this group, 1 in every 1,000 children developed autism, compared with 2 in every 1,000 children born to women who didn’t take these supplements.

After factoring in other things that might affect the risk of autism, the researchers estimated that children whose mothers took folic acid were nearly 40 percent less likely to develop this disorder.

The researchers didn’t find a link between folic acid and other types of ASDs. However, this may have been because too few children developed these disorders in the study to show a link. Overall, 270 children were diagnosed with an ASD during the study, including 114 with autism, 56 with Asperger’s syndrome, and 100 with PDD-NOS.

How reliable is the research?

This type of study can’t prove that folic acid reduces the risk of autism. It can show only that there may be a link. This is because we can’t be certain that there wasn’t something else about women who took folic acid that lowered their children’s risk.

For example, women who take supplements tend to be more health-conscious in general, and this might have played a role. The researchers did a separate analysis to explore this, where they looked at whether children born to women who took fish oil supplements also had a similarly reduced risk of autism. If the answer was yes, that would suggest that the reduction in risk was down to healthier living in general, rather than the individual supplements. However, the researchers found no link between fish oils supplements and autism. This makes it more likely that the link with folic acid is genuine.

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