Vitamin C in pregnancy may reduce wheeze in infants

3 minute read

But that doesn’t let the one in 10 pregnant Aussies who smoke off the hook, experts say.

Infants whose mothers smoked during pregnancy may be less likely to have early signs of asthma if their mothers also took vitamin C, research suggests.

Almost 9% of Australian women reported smoking at some point during pregnancy, according to the Australian Institute of Health and Welfare’s 2021 data. Figures from the 2019 National Drug Strategy Household Survey show that 22% of women said they smoked before they knew they were pregnant, and 11% smoked after they found out they were pregnant.    

The US researchers found that babies of women who smoked and took 500mg of vitamin C during pregnancy had fewer reports of wheeze compared to the offspring of smokers who did not take vitamin C.

Asthma is difficult to diagnose in young children, so wheeze is measured as an indicator for the future presence of asthma.

The study, published in a research letter in JAMA Pediatrics, measured forced expiratory flows (FEFs) in 243 children using spirometry when the infants were three, 12, and 60 months of age.

They also tracked the infants’ wheeze using respiratory questionnaires every three months.

The researchers said the children in the vitamin C group had a greater increase in FEFs between 25% and 75% (FEF25%-75%) expired volume as they got older. They said wheeze occurrence was significantly lower in the vitamin C group and those infants had a significant decrease in wheeze at four to six years of age.

“Vitamin C supplementation to women who smoked during pregnancy resulted in an increased FEF25%-75% trajectory in offspring through five years of age,” they wrote.

“The difference in FEF25%-75% between the treated groups increased with increasing age despite no postnatal supplementation.

“The vitamin C group had a lower wheeze occurrence at four to six years of age, and this improved clinical outcome appears to be mediated through the effect of vitamin C on improved airway function at five years of age.”

Respiratory disease researcher Professor Brian Oliver, head of the Molecular Pathogenesis Group, Respiratory Cellular and Molecular Biology at the Woolcock Institute, told TMR that not everyone agreed with the findings.

“It’s very difficult to show positive effects of vitamin C supplementation on health effects,” said Professor Oliver.

“The other difficult concept here is smoking during pregnancy. Just because these studies show positive effects of vitamin C, that doesn’t mean that the other health risks associated with smoking during pregnancy are also reduced.”

Maternal smoking during pregnancy was the largest modifiable risk factor for the development of asthma, Professor Oliver told TMR.

“We know that smoking during pregnancy is really bad for the baby, causing what is referred to as placental insufficiency, resulting in the baby being starved of nutrients and being born underdeveloped (small for gestational weight) and at high risk of a range of diseases including childhood asthma,” he said.

JAMA Pediatrics 2024, online 8 April

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