This was a purely observational study, and so it cannot provide evidence of causal effects, as the authors rightly emphasise.
Nonetheless, the association of folic acid supplementation in early pregnancy with a reduced risk of severe language delay in the resulting children is consistent with what is already known about the importance of this B vitamin for brain development.
These findings clearly merit further investigation, but meanwhile they add further weight to existing public health recommendations about the importance of folic acid supplementation for the prevention of neural tube defects.
For further details of this study, see:
Women who took folic acid supplements in the first two months of pregnancy were less likely to have kids with severe language delays in a new study from Norway
Folic acid is already known to reduce the risk of certain types of birth defects, and both the U.S. and Canada fortify grain products with folic acid to make sure pregnant women get enough of it. But that's not the case in some other countries, including Norway, and doctors still worry about pregnant women getting enough of the B vitamin -- especially in the developing world.
"We don't think people should change their behavior based on these findings," said Dr. Ezra Susser from Columbia University's Mailman School of Public Health in New York, who worked on the study.
"But it does add weight to the public health recommendation to take folic acid early in pregnancy," he told Reuters Health.
And, he added, it shows that "what you do during pregnancy... is not only important for birth but also for subsequent development."
The researchers gave surveys to close to 40,000 Norwegian women a few months into their pregnancies. Those included questions on what supplements women were taking in the four weeks before they got pregnant through eight weeks after conception.
Then, when their kids were three years old, Susser and his colleagues asked the same women about kids' language skills, including how many words they could string together in a phrase.
Toddlers who could only say one word at a time or who had "unintelligible utterances" were considered to have severe language delay. In total, about one in 200 kids fit into that category.
Four out of 1,000 kids born to women who took folic acid alone or combined with other vitamins had severe language delays. That compared to nine out of 1,000 kids whose moms didn't take folic acid before and early in pregnancy.
The pattern remained after Susser's team took into account other factors that were linked to both folic acid supplementation and language skills, such as a mom's weight and education, and whether or not she was married.
The researchers didn't find any link between folic acid during pregnancy and kids' motor skills, measured by how well toddlers could kick or catch a ball.
The study can't prove that folic acid, itself, prevents language delay, they wrote in the Journal of the American Medical Association. But Susser said the vitamin is known to affect the growth of neurons and could influence how proteins are made from certain genes.
"Clearly it plays a role in development that starts very early in pregnancy," said Usha Ramakrishnan, a maternal and child nutrition researcher from Emory University in Atlanta who wasn't involved in the new study.
However, she added, it's hard to separate out exactly when during pregnancy folic acid supplements would have an effect on later language development -- since women who are taking supplements early are more likely to take them throughout pregnancy.
Susser said the results likely apply in the U.S. and other countries where grains are fortified with folic acid, also called folate, because extra supplements are still recommended during pregnancy. But he added that more research is needed to support the new study.
"The recommendation worldwide is that women should be on folate supplements through all their reproductive years," Susser said. Because of that, "we really need to know what the impact is on children, both benefits and risks."
"I think this adds to what's already known about the benefits of folic acid," Ramakrishnan told Reuters Health. "It gives one more positive message of potential benefit."