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BARCELONA -- Taking high-dose vitamin D and fish oil during pregnancy reduced the risk of croup in young children, a Danish randomized controlled trial showed.

Among over 600 pregnant women, taking fish oil led to a 38% reduced risk of croup in kids under 3 years old compared with placebo (HR 0.62, 95% CI 0.41-0.93, P=0.02), while taking high-dose vitamin D led to a 40% reduction in croup risk versus standard-dose vitamin D (HR 0.60, 95% CI 0.38-0.93, P=0.02), reported Nicklas Brustad, MD, PhD, of the University of Copenhagen in Denmark, during the European Respiratory Society meeting.

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

"We are not sure of the exact mechanisms behind the beneficial effects of vitamin D and fish oil, but it could be that they can stimulate the immune system to help babies and young children clear infections more effectively," he added.

However, there was no evidence of an interaction between supplements. Levels of risk reduction were similar with both supplements, but there was no additive effect (P_interaction=0.56).

"If you receive either one of the interventions of fish oil or vitamin D, you actually come out with the same risk for the children up to the first 3 years of life," Brustad said during his presentation. "So, it kind of suggests a ceiling effect of these two interventions."

Croup is a common acute respiratory disease in childhood from the age of 6 months to 3 years, Brustad explained. It is mainly caused by parainfluenza viruses, for which there are no vaccines. While it is often a mild disease, severe cases can lead to hospitalization, especially in children with asthma and immunodeficiencies.

Since fish oil and vitamin D are thought to play a role in the development of the immune system and lung maturation, it has been hypothesized that taking these supplements during pregnancy may result in a reduced risk of croup in children.

A question from the audience during the Q&A session raised a potential concern about toxic vitamin D levels, but Brustad said that no such levels were reached in mothers or their children during the study.

For this double-blind randomized controlled trial, the researchers included 623 pregnant Danish women. Randomization was performed at week 24 of gestation.

The women were divided into four groups to test the effectiveness of both supplements together and separately:

• High-dose vitamin D (2,800 IU/day) and fish oil (2.4 g)
• Standard-dose vitamin D (400 IU/day) and fish oil (2.4 g)
• High-dose vitamin D (2,800 IU/day) and olive oil (used as a placebo for fish oil due to their similar appearance)
• Standard-dose vitamin D (400 IU/day) and olive oil

Children were followed for the first 3 years through nine planned visits and when experiencing acute respiratory symptoms. A total of 97 cases of croup occurred among the children.

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