Taking folic acid during pregnancy may not boost the risk of your child developing asthma or allergies later in life, according to a study adding to the mixed bag of research on the question.
Women of child-bearing age are told to get 400 micrograms of folic acid a day. The goal is to prevent neural tube defects—severe birth defects of the brain and spine that include spina bifida (where the spine fails to close during fetal development) and anencephaly (a usually fatal defect where much of the brain never forms).
Experts say women should get that much folic acid even before becoming pregnant, since neural tube defects take shape very early in the fetus' development, before many women know they are pregnant.
A few studies, though, have linked folic acid during pregnancy to a heightened risk of asthma symptoms in young children.
Those studies only show a correlation, and don't prove cause and effect. But they have raised some concerns, especially since there is also animal research suggesting that folic acid could affect fetal immune system development.
But in this latest study, published in the European Respiratory Journal, Dutch researchers were unable to find a correlation between folic acid and asthma risk in children up to age eight.
Of more than 3,200 children in the study, 13 percent had asthma symptoms at that age. And there was no difference between children whose mothers had used folic acid during pregnancy and those whose mothers had not.
Mothers' folic acid use was linked to a small increase in the risk of wheezing in a baby's first year, but not with any respiratory symptoms after the age of 1.
"The benefits of folic acid supplementation for the prevention of neural tube defects are well established," lead researcher Marga Bekkers, of Utrecht University in the Netherlands, told Reuters Health in an email.
On the other hand, a link between folic acid and asthma is not well established. Bekkers pointed to another Dutch study published earlier this year that found no association.
But the story is not over, according to Dr. Michael Davies, an associate professor at the University of Adelaide in Australia.
In a study out last year, Davies and his colleagues found that folic acid late in pregnancy -- from the 30th week on—was associated with an increased risk of asthma symptoms in three- to five-year-olds.
In an email to Reuters Health, Davies agreed that folic acid use in early pregnancy is important, and "there are no data contradicting" that advice.
"However," he added, "continued supplementation beyond week 8 cannot reduce the risk of neural tube defects. It's simply too late."
And there's recent evidence, Davies said, that folic acid may have "very complex modes of action," affecting gene expression and, possibly, immune system development. And since the fetal immune system develops later in pregnancy, folic acid at that point could—in theory—have some effect on later asthma risk.
Davies' study was, however, the first to link late-pregnancy folic acid to children's asthma. And more research is needed to back it up.
According to Davies, a limitation of the human studies so far is that none, to his knowledge, were specifically designed to find out whether folic acid during pregnancy is related to children's asthma risk.
Instead, they have looked back at data from older studies designed with other goals. Children in the current study were part of a project begun in 1996 looking at whether mattress and pillow covers helped cut the risk asthma and allergy in kids.
"There is now an imperative to design new studies to comprehensively examine the matter," Davies said.
In his team's study, there was no connection between foods rich in folate (the natural form of folic acid) and children's asthma risk. That, the researchers said, should encourage women to eat those foods throughout pregnancy.
High-folate foods include beans and lentils, orange juice and green vegetables like spinach and broccoli.