The risk of croup in infants may be reduced by maternal consumption of fish oil and vitamin D during pregnancy, evidence from a European randomised controlled trial has shown.

Findings presented at the European Respiratory Society International Congress in Barcelona (ERS 2022), showed that the risk of croup before the age of three was reduced by up to 40% among infants whose mothers took vitamin D and fish oil in high doses in pregnancy.

The Copenhagen Prospective Studies on Asthma in Childhood (COPSAC) study included 736 pregnant women who were randomised to receive high-dose vitamin D supplement (2800 international units per day) and fish oil containing long-chain n-3-polyunsaturated fatty acids (2.4 grams), or either of these plus a control intervention (olive oil or standard-dose vitamin D).

In the blinded study, all the women took the supplements daily from their 24th week of pregnancy until one week after their babies were born.  Offspring were monitored until they were three years old and any who were suspected of having croup were diagnosed by a doctor or via their medical records. There was a total of 97 cases of croup amongst the children.

Overall, children whose mothers took the fish oil had an 11% risk of croup, compared to 17% in the children whose mothers took olive oil (a 38% decrease).

Children whose mothers took high-dose vitamin D had an 11% risk of croup, compared to an 18% risk in those whose mothers took the standard-dose vitamin D (a 40% decrease).

Study investigator Dr Nicklas Brustad, a clinician and postdoctoral researcher at Copenhagen University Hospital, told the Congress it wasn’t certain by which what mechanism vitamin D and fish oil could prevent croup but both were known to have a potential upregulating effect on immune responses.

“There is currently no vaccine against the pathogen that causes this disease. Therefore, other preventive strategies are needed, and measures initiated during pregnancy might be important since croup occurs in babies and young children,” he said.

“Our findings suggest that vitamin D and fish oil could be beneficial against childhood croup in sufficiently high doses. These are relatively cheap supplements meaning that this could be a very cost-effective approach to improving young children’s health.

Professor Rory Morty from the University of Heidelberg is chair of European Respiratory Society’s lung and airway developmental biology group and was not involved in the research.

He said: “We know that lung health in babies and young children can be influenced during pregnancy. For example, babies whose mothers smoke tend to have worse lung health. We are increasingly seeing that elements of a mother’s diet can also help or hinder a baby’s lung development.

“This research suggests that taking vitamin D and fish oil supplements during pregnancy could have benefits for babies and young children. We would like to see further research in this area to support these findings as this could lead to new recommendations for supplementation during pregnancy. Pregnant women should always speak to their doctor before taking supplements.”