In a previous trial, the investigators found that vitamin C significantly improved pulmonary function tests and improved airway function at 3 months among infants born to people who smoked during pregnancy.
The current study, published in JAMA Pediatrics, followed up 213 children born to 251 women who smoked and were treated with 500 mg/d of vitamin C or placebo. The study compared their forced expiratory flow (FEF) measurements and occurrence of wheeze at the age of five.
The study’s primary outcome was FEF between 25% and 75% expired volume (FEF25-75) by spirometry at age five. Secondary outcomes included FEF measurements at 50% and 75% of expiration (FEF50 and FEF75), forced expiratory volume in the first second (FEV1), and occurrence of wheeze.
Results indicate the children in the vitamin C group had a 17.2% improvement in their FEF25-75 and a 40% decrease in occurrence of wheeze compared with the placebo group. Both groups, however, had a high occurrence of wheeze, “which highlights the high respiratory morbidity associated with in utero smoke exposure,” the authors wrote. Average measurements among children in the vitamin C group were increased by 14.1% for FEF50, 25.9% for FEF75, and 4.4% for FEV1.
Vitamin C appeared to have a greater effect on the occurrence of wheeze when the supplement was taken before 18 weeks of gestation, suggesting that the timing of the intervention during foetal lung development may be important. The authors noted that airway function in childhood may be an important risk factor for the development of chronic obstructive pulmonary disease in adulthood.
The initial study screened 1,225 pregnant women who continued to smoke in pregnancy; 892 were excluded before consent, and 81 were excluded after the medication adherence period. The team randomised 251 women (125 who received vitamin C (500 mg/d) and 126 who received placebo). Randomization balanced relevant baseline covariates including age, race and ethnicity, parity, and gestational age.
The infants born to the smokers randomised to vitamin C had a significantly increased FEF50 and FEF25–75 compared with those randomised to placebo. There was also a significant difference in FEV0.5 between the groups.
The researchers concluded: "Although our primary outcome of FEF75 at 3 months of age was not improved after vitamin C supplementation to pregnant smokers, the related measures FEF50 and FEF25–75 obtained from the same forced expiratory curve were significantly improved. This extends our previous findings of improved newborn PFTs in infants of pregnant smokers randomized to vitamin C versus placebo."
Source: JAMA Pediatrics
"Effect of Vitamin C Supplementation for Pregnant Smokers on Offspring Airway Function and Wheeze at Age 5 YearsFollow-up of a Randomized Clinical Trial"
Authors: Cindy T. McEvoy, MD, MCR; Lyndsey E. Shorey-Kendrick, PhD; Kristin Milner, BA; et al