Why does wheezing decrease in children of smokers when mothers take vitamin C during pregnancy?

Improved airway function appears to mediate the association between vitamin C supplementation and wheezing in children whose mothers smoked and took vitamin C during pregnancy, a secondary analysis of clinical trial data found. found.

Longitudinal analysis of forced expiratory flow between 25% and 75% of expiratory volume (FEF)_25%-75%) At 3 years, 12 months, and 60 months, children whose mothers took vitamin C had significantly higher levels compared to children whose mothers received a placebo (P<0.001), significant increase in FEF_25%-75% Cindy McEvoy, MD, MCR, of Oregon Health & Science University in Portland, and co-authors reported that this condition increases with age, even though women do not receive postpartum supplements.

Children in the vitamin C group between 4 and 6 years of age had a significantly lower incidence of wheezing (OR 0.41, 95% CI 0.23-0.74; P=0.003).More than half (54.2%) of the association between vitamin C and wheezing was mediated by the association between vitamin C and increased FEF_25%-75%the researchers said. JAMA Pediatrics.

“Our findings provide evidence of a direct association between maternal smoking during pregnancy and the development of wheezing in children,” McEvoy and colleagues wrote.

Exposure to smoke in utero is a risk factor for decreased respiratory function later in life. In the United States, the percentage of mothers who smoked during pregnancy has decreased over time, and the latest CDC report found that in 2021, the smoking rate was 4.6%.

McEvoy and colleagues randomly assigned women who smoked during pregnancy to receive 500 mg/day of vitamin C or a placebo in the Vitamin C Trial to Reduce the Effects of Smoking During Pregnancy on Infant Lung Function. VCSIP) data were evaluated. Follow-up studies showed that children up to the age of five whose mothers took vitamin C during pregnancy had improved airway flow and reduced wheezing.

In both the vitamin C and placebo cohorts, mothers smoked approximately 8 cigarettes per day in the week before enrollment and subsequently smoked approximately 10 cigarettes per day by the time their child was 1 year old. .

The researchers included spirometry FEF measurements taken when the offspring were 3 months, 12 months, and 60 months old in their analysis. Wheezing was assessed quarterly through a standardized respiratory questionnaire.

A total of 243 offspring were born during the study period, of which 233 had at least one FEF measurement. Most children (80%) who had data at 60 months also had data at 3 or 12 months.

The offspring population was 49.8% female and 50.2% male. Most (79.4%) were Caucasian. 12.4% were Black or African American, 6.4% were of multiple races, 1.3% were American Indian or Alaska Native, and 0.4% were Native Hawaiian or other Pacific Islander.

There were no significant differences in height, gender, race, or postnatal smoking exposure (assessed by report and hair analysis) at each age.

The researchers acknowledged that wheezing in pediatric patients may be difficult to recognize, which may have influenced the results.

“The vitamin C group had a greater increase in FEF;_25%-75% From 3 months to 5 years of age, follow-up is required to determine if FEF_25%-75% “It continues to increase beyond the age of five,” they noted.