Daily vitamin C during smokers’ pregnancies significantly improved the lung function of their infants at birth and reduced the incidence of wheezing during the first year of life, compared with infants of smokers who weren’t exposed to the vitamin.
Those infants had significantly poorer respiratory outcomes, both at birth and 1 year, according to Dr. Cindy McEvoy and colleagues. The study was presented at an international conference of the American Thoracic Society and simultaneously published in the May 18 issue ofthe Journal of the American Medical Association.
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Pregnant smokers who took vitamin C daily improved the lung function in their infants, a new study reports.
While it’s not entirely clear how vitamin C influences prenatal lung development, there are tantalizing hints, wrote Dr. McEvoy of the Oregon Health and Science University, Portland, and her coinvestigators. "Supplemental vitamin C may act by blocking formation of reactive oxygen species, which stimulate abnormal patterns of airway cell proliferation, resulting in narrowed airways and abnormal airway geometry," they said.
Dr. McEvoy and her team randomized 179 pregnant smokers to either placebo or 500 mg vitamin C daily from week 16 of pregnancy. At birth, they examined two respiratory function measures: the ratio of time to peak expiratory flow/expiratory time (TPTEF:TE) and passive respiratory compliance per kg (Crs/kg). They also compared the incidences of wheezing during the first year. A control group of 76 infants from nonsmokers provided a comparator (JAMA 2014 May 18 [doi:10.1001/jama.2014.5217]).
The women were a mean age of 26 years at baseline. Most were white (about 85%), and 20% had at least some college education. In the placebo group, 36% smoked at least 10 cigarettes a day; in the active group, 41% smoked that many. All smoking mothers were offered the chance to participate in a smoking cessation program; 10% were able to stop.
At birth, infants exposed to vitamin C had significantly better lung function than nonexposed infants on both measures. The TPTEF:TE was 10% better in the exposed group (0.383 vs. 0.345) – similar to the ratio in the comparator group of infants from nonsmoking mothers. The Crs/kg was also significantly better (11%) in the vitamin C group (1.32 vs. 1.20 mL/cmH20/kg).
Almost all of the babies had 1-year follow-up (92%). At that time, the incidence of wheezing during the first year was 21% in the treated group and 40% in the placebo group (adjusted relative risk, 0.56). However, the authors noted, there was no between-group difference in the other lung function measures at 1 year.
A subgroup of 173 mothers was genotyped for two polymorphisms that are strongly associated with a lifelong risk of nicotine addiction, lung cancer, and chronic obstructive pulmonary disease.
The infants of mothers who were heterozygous for one of those (rs16969968), experienced the largest benefit from vitamin C exposure. The incidence of wheezing through 1 year in these infants was 14%, compared with 48% among those randomized to placebo.
The National Heart, Lung, and Blood Institute sponsored the study. Neither Dr. McEvoy nor any of her coauthors had any financial disclosures.