Australian researchers say they may have found a link between folate supplements taken during late pregnancy and asthma in young children.
The Adelaide University study shows that children aged between three and five years are more likely to have asthma if their mothers have taken the supplements after their first trimester, the ABC reports.
Associate Professor Michael Davies says the link was only found with folate supplements and not dietary folate, which is available in green, leafy vegetables.
He says folate is still very important in early pregnancy and more studies need to be done.
"Folate's an incredibly important nutrient; it's actually critical for the survival of every cell in our body.
"But it appears to have a range of effects and it even appears now to have some unexpected effects when taken in high doses at not necessarily the best time."
The results of the study have just been published in the American Journal of Epidemiology.
The New Zealand Government announced earlier this year that mandatory inclusion of folate in bread will be deferred to 2011.