Vitamin C Supplementation Among Pregnant Smokers and Airway Function Trajectory in Offspring: A Secondary Analysis of a Randomized Clinical Trial

The Vitamin C to Decrease Effects of Smoking in Pregnancy (VSCIP) study showed that vitamin C supplementation in pregnant women was associated with increases in their children’s forced expiratory flow (FEF) at 3 and 12 months, with follow-up study at 60 months associated with higher FEF and lower occurrences of wheezing. The association between FEF trajectory and wheeze occurrence at age 4 to 6 years is unknown.A total of 243 children of pregnant smokers were randomized to receive vitamin C supplementation (500 mg/d) or placebo at 3 large academic medical centers. There was no postnatal vitamin C supplementation.Post hoc longitudinal analysis was performed on the VSCIP cohort with spirometry recorded at 3, 12, and 60 months and wheeze occurrences assessed in quarterly questionnaires. Mediation analysis was used to determine association between FEF25%–75% quartile, vitamin C treatment, and incidence of wheezing.There were statistically significant increases in FEF25%–75% in the vitamin C group compared with placebo, with increasing differences in FEF with age. Vitamin C supplementation was associated with fewer occurrences of wheezing. Vitamin C association with decreased wheeze was mediated through the increases in FEF.There was a significant difference in lung function trajectory between the children exposed to vitamin C in utero vs placebo, and these differences increased with age. Lower occurrences of wheezing seen in children aged 4 to 6 years exposed to vitamin C are likely mediated through differences in lung function at that age.Vitamin C supplementation in pregnant women who smoke may improve lung function and decrease frequency of wheezing in their children. This may be considered for mothers who smoke and have a strong family history of asthma who are interested in modifying asthma risk in their offspring.