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Vitamin C Supplementation for Pregnant Smoking Women and Pulmonary Function in Their Newborn Infants: A Randomized Clinical Trial
Study Questions:
Does vitamin C supplementation to pregnant smokers improve pulmonary function for their newborns?
Methods:
This was a randomized, double-blind trial, which enrolled participants from three sites in the Pacific Northwest between March 2007 and January 2011. Pregnant women were included if they were 15 years or older, current smokers (≥1 cigarette per day), had a single gestation, and were randomized at 22 weeks or less gestational age by last menstrual period. All participants had declined smoking cessation. Pregnant women were randomized to receive vitamin C (500 mg/day) or placebo. The primary outcome of interest was newborn pulmonary function (ratio of the time to peak tidal expiratory flow to expiratory time [TPTEF:TE] and passive respiratory compliance per kilogram [Crs/kg]) within 72 hours of age. Secondary outcomes included incidence of wheezing through age 1 year and pulmonary function test (PFT) results at age 1 year. A subgroup of pregnant smokers and nonsmokers had genotyping performed.
Results:
A total of 159 newborns of pregnant smokers (76 received vitamin C and 83 placebo) were included. At study entry, 41% of the vitamin C group and 36% of the placebo group reported smoking 10 or more cigarettes per day. No significant difference in urine cotinine levels was observed. The average medication adherence was 81% in the vitamin C group and 82% in the placebo group. Newborns of women randomized to vitamin C (n = 76), compared with those randomized to placebo (n = 83), had improved pulmonary function, as measured by TPTEF:TE (0.383 vs. 0.345; adjusted 95% confidence interval [CI] for difference, 0.011-0.062; p = 0.006) and Crs/kg (1.32 vs. 1.20 ml/cm H2O/kg; 95% CI, 0.02-0.20; p = 0.01). Offspring of women randomized to vitamin C had significantly decreased wheezing through age 1 year (15/70 [21%] vs. 31/77 [40%]; relative risk, 0.56; 95% CI, 0.33-0.95; p = 0.03). There were no significant differences in the 1-year PFT results between the vitamin C and placebo groups. The effect of maternal smoking on newborn lung function was associated with maternal genotype for the α5 nicotinic receptor (rs16969968) (p < 0.001 for interaction).
Conclusions:
The investigators concluded that supplemental vitamin C taken by pregnant smokers improved newborn PFT results and decreased wheezing through 1 year in the offspring. Vitamin C in pregnant smokers may be an inexpensive and simple approach to decrease the effects of smoking in pregnancy on newborn pulmonary function and respiratory morbidities.
Perspective:
These results suggest that supplementation with vitamin C, which is affordable to most adults, translates into significant benefits for newborns of smoking mothers.
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