Daily supplements of vitamin C might mitigate some of the harm to fetal lung development from smoking during pregnancy, according to a study.
At 3-months of age, infants born to pregnant smokers who took 500 mg/day of vitamin C in addition to a standard prenatal vitamin had significantly better lung function by some measures of forced expiratory flow (FEF) than did babies born to smokers randomized to receive placebo instead of the vitamin C.
At 3-months of age, infants whose mothers took the vitamin C supplements had better FEF50 (436.7 vs 408.5 mL/sec, P=0.02) and FEF25-75 (387.4 vs 365.8 mL/sec, P=0.04).
However, the trial missed the primary endpoint of improving FEF75 (200.7 vs 188.7 mL/sec, P=0.10), a flow obtained from the same expiratory curve as the other measures, Cindy McEvoy, MD, of the Oregon Health & Science University in Portland, and colleagues, reported in the American Journal of Respiratory and Critical Care Medicine.
An earlier study had shown vitamin C supplementation protective in a group of newborns (72 hours old) born to women who smoked during pregnancy. But that study used passive measures to assess lung function, lead researcher McEvoy told MedPage Today.
The first focus of the clinician caring for pregnant smokers is to try to convince them to give up the habit, McEvoy stressed. But, she added, the reality is that many women can’t or won’t stop smoking during pregnancy.
It is estimated that around 10% of pregnant women in the U.S. smoke during pregnancy, and in some populations the percentage is as high as 30% or 35%, she said.
“Many of the women in our study started smoking at really young ages,” she said. “Pregnant smokers tend to come from more disadvantaged populations and they tend to have more comorbidities. Some of (the mothers in the study) also had other addictions that they were focusing on overcoming. They would have liked to quit smoking, but there is only so much you can do.”
Throughout the randomized trial, the pregnant participants received smoking cessation counseling, and about 10% quit smoking during the study.
The double-blind, placebo-controlled trial was conducted at three centers and included 251 pregnant smokers randomized at 13 to 23 weeks of gestation to vitamin C (500mg/day) or to placebo.
Current smoking was defined as smoking one or more cigarettes during the prior week.
Outcomes included FEF75 at 3 months of age performed with the raised volume rapid thoracic compression technique, FEF50 and FEF25-75 obtained from the same expiratory curves.
Infant FEFs were associated with the genetic variant α5 nicotinic acetylcholine receptor (α5 nAChR) that appeared to amplify the negative impact of nicotine on babies. The genetic variant has been linked to an increased risk for lung cancer and obstructive lung disease in other studies.
“This confirms and expands our initial study of improved newborn PFTs with similar findings but in a larger population with increased diversity through the measurement of FEFs, a more specific measurement of airway function. We also confirm our previous findings of the importance of the α5 nAChR in the effect of in-utero smoke on pulmonary function,” she said.
McEvoy told MedPage Today that the findings support the hypothesis that oxidative mechanisms are, at least in part, responsible for the effects of in-utero nicotine on lung development.
At randomization, both groups of pregnant smokers in the study had levels of fasting ascorbic acid of 49 μmol/L that were decreased compared to levels reported for nonsmoking women (58 μmol/L), consistent with the increased oxidative load associated with smoking.
Pregnant women randomized to the supplemental vitamin C had significantly increased fasting ascorbic acid levels at 26 and 32 weeks of gestation when compared to baseline similar to levels typically reported in nonsmoking women.
The research was funded by the National Heart, Lung, and Blood Institute and the Office of Dietary Supplements.