Australian guidelines recommend expecting mothers to take folic acid—a type of vitamin B—during the first trimester of pregnancy to aid the development of the baby’s central nervous system.
However, researchers at Adelaide University’s Robinson Research Institute found growing evidence that continued supplementation into the later stages might actually increase the risk of allergies in offspring.
Previous research has shown that a complication of pregnancy known as intrauterine growth restriction (IUGR)— growth restriction in the womb often resulting in low birthweight, and in the worst cases stillbirth—may have a protective effect against childhood allergies.
In the latest study, the Adelaide team measured the skin reactions of sheep born from normal or growth-restricted pregnancies to dust mites and egg whites—two common allergens.
But when sheep with growth-restricted pregnancies were fed folic acid supplements late in pregnancy, their offspring lost that advantage.
“[They] were less likely to have allergic reactions to egg white protein than those born to normal pregnancies,” said Kathy Gatford, a member of the study team.
“Importantly, if the sheep with growth-restricted pregnancies were fed supplements containing folic acid in late pregnancy, their offspring had similar rates of allergic reactions as control progeny,” she added.
Allergies are estimated to affect 30-40% of the global population, and are among the main causes of non-communicable diseases in the world. Susceptibility to these diseases after birth is partly determined by an individual’s early life environment.
In the future, animal models based on the Adelaide study will allow scientists to investigate directly the effects of the environment before birth on later allergy. However, according to Dr Gatford, more research will be needed before any recommendations regarding the right timing of supplementation could be made in humans.
"We are now in the process of analysing how a growth-restricted pregnancy and the dietary supplement affect the nutrient status of offspring at birth, and how this might switch on or off genes that regulate the immune system,” she added.
The National Health and Medical Research Council-funded research is published online ahead of print in the American Journal of Physiology—Regulatory, Integrative and Comparative Physiology.