Public health guidlines already emphasis the importance of supplementation with folic acid (the synthetic form of folate, vitamin B9) for all women of childbearing age, as insufficient intakes in early pregnancy are known to raise the risk of spina bifida or other serious neurological disorders.
This population study adds to existing evidence suggesting that folic acid supplementation might also help to reduce the risk of autistic spectrum disorders (although as the authors emphasise, this kind of study design cannot provide definitice evidence of cause-and-effect).
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A new study suggests that women who start taking folic acid supplements either before or early in their pregnancy may reduce their child's risk of developing autism.
"The study does not prove that folic acid supplements can prevent childhood autism. But it does provide an indication that folic acid might be preventive," said study lead author Dr. Pal Suren, from the division of epidemiology at the Norwegian Institute of Public Health in Oslo.
"The findings also provide a rationale for further investigations of possible causes, as well as investigations of whether folic acid is associated with a reduced risk of other brain disorders in children," he said.
Taking folic acid supplements during pregnancy is already known to prevent birth defects such as spina bifida, which affects the spine, and anencephaly, which causes part of the brain to be missing.
Alycia Halladay, senior director of environmental and clinical sciences at Autism Speaks, said that "parents always wonder what they can do to reduce the risk (of autism), and this (folic acid) is a very inexpensive item that mothers can do both before pregnancy and very early in their pregnancy."
As to why folic acid may be beneficial, Halladay speculated that the nutrient might blunt a genetic risk for autism or boost other processes during pregnancy that are protective.
Another expert, Dr. Roberto Tuchman, director of the Autism and Neurodevelopment Program at Miami Children's Hospital's Dan Marino Center, said, "This study suggests that in some kids autism spectrum disorders may be preventable. As a clinician who works with autism spectrum disorders it is exciting that we can look at potentially preventable factors in autism. This is really encouraging."
Still, Tuchman cautioned that the study findings are very preliminary, and it isn't possible to tell which autism spectrum disorders, if any, folic acid may prevent.
The study findings were published in the Feb. 13 issue of the Journal of the American Medical Association.
To see whether folic acid might protect children from autism, Suren's team collected data on more than 85,000 children born in Norway from 2002 to 2008.
Over an average of six years of follow-up, 270 children were diagnosed with autism spectrum disorders, 114 with autism, 56 with Asperger syndrome and 100 with an unspecified autism disorder.
Among those mothers who took folic acid supplements, 0.10 percent of their children were diagnosed with autism, compared with 0.21 percent of children whose mothers didn't take folic acid. That's a 39 percent lowered risk for the neurodevelopment disorder, Suren said.
Women who took the supplements were more likely to be better educated and have planned their pregnancy. They were also likely to be thin and not smoke. For most, it was their first child, the researchers added.
Suren's group did not find a connection between folic acid and either Asperger syndrome or unspecified autism disorder. "For Asperger syndrome, the number of children was too low to obtain sufficient statistical power in the analyses," Suren explained.
The protective affect of folic acid seemed to work even if not taken until early pregnancy. No protection from folic acid was seen if taken at mid- pregnancy, the researchers noted.
"The results support the current recommendations of taking folic acid supplements during pregnancy and emphasize the importance of starting early, preferably before conception," Suren said.
Halladay said the study finding confirms the results of another study that showed that folic acid might reduce the risk of autism. "The benefits of prenatal care, including taking vitamins, has been well-documented for things like birth defects and even language delay," she said.
Whether or not folic acid supplementation will make a dent in the growing number of children diagnosed with autism spectrum disorder isn't known. An estimated one in 88 children in the United States has been diagnosed with some form of autism spectrum disorder, according to the federal Centers for Disease Control and Prevention.
In the United States and other countries many foods, such as breads and pasta, are fortified with folic acid to help prevent birth defects. But, it isn't clear yet how much folic acid might guard against autism, so a woman should discuss her options with her doctor, Halladay said.