A University of Adelaide study may have shed light on the rise in childhood asthma in developed countries like Australia in recent decades.
Researchers from the University's Robinson Institute have identified a link between folic acid supplements taken in late pregnancy and allergic asthma in children aged between 3 and 5 years, suggesting that the timing of supplementation in pregnancy is important.
Associate Professor Michael Davies says that folic acid supplements - recommended for pregnant women to prevent birth defects - appear to have "additional and unexpected" consequences in recent studies in mice and infants.
"In our study, supplemental folic acid in late pregnancy was associated with an increased risk of asthma in children, but there was no evidence to suggest any adverse effects if supplements were taken in early pregnancy."
The University of Adelaide findings have been published in the American Journal of Epidemiology.
The study involved more than 500 women whose maternal diet and supplements were assessed twice during their pregnancy, with follow-up on their child's asthma status at 3.5 years and 5.5 years. Asthma was reported in 11.6% of children at 3.5 years and 11.8% of children at 5.5 years. Nearly a third of these children reported persistent asthma.
Current public health guidelines recommend that women consume a supplemental dose of 400 micrograms of folic acid per day in the month preceding and during the first trimester of pregnancy to reduce the risk of neural tube defects in children.