In a previous study, the researchers reported that daily supplemental vitamin C in pregnant women who could not quit smoking improved their newborn’s pulmonary function as measured by passive respiratory compliance and the time to peak tidal expiratory flow to expiratory time.
At one year, the study also found that babies whose mothers took vitamin C were less likely to develop wheeze.
In the newest study, the researchers measured force expiratory flows (FEFs) at 3 and 12 months of babies born to 252 mothers who smoked. FEF measures the speed with which air can be forced out of the lung.
The mothers who smoked were randomized to either receive 500 mg of supplemental vitamin C every day or a placebo in addition to the same prenatal vitamin.
They were encouraged throughout their pregnancies to quit smoking. On average, the mothers in both arms of the study who could not quit smoked seven cigarettes a day.
“We performed FEFs in this study because they provide a more direct measurement of actual air way function, and are more predictive of future disease,” said lead study author Cynthia McEvoy, MD.
“Because infants are not cooperative at 3 and 12 months of age, we had to use sophisticated testing techniques to get these results, but they are similar to the results you would get when doing a spirometry test.”
The researchers measured FEFs at three intervals defined by the percentage of air remaining in the lung during forced exhalation: FEF75, FEF25-75 and FEF50.
At three months, there was a statistically significant difference in lung function between the babies born to the two groups of women at the FEF25-75 and FEF50 intervals.
At 12 months, there was a statistically significant difference in lung function between the two groups of babies at all three intervals.
The study did not find a significant difference between the two groups of babies in gestational age at delivery, delivery mode, incidence of prematurity or birthweight.
The researchers said that they are not certain why vitamin C has this protective effect on the lungs but are focusing on this question in continuing research.
Study co-investigator Eliot Spindel, MD, PhD, speculates that it may “block the increased collagen deposition around the airways that has been shown in animal models of babies born after smoke/nicotine exposure during pregnancy, which likely makes the lungs and airways stiffer” and/or “prevent some of the epigenetic changes that contribute to the lifelong effects of in-utero tobacco exposure.”
The study will follow the children until they are six years old to see if vitamin C has a long-term effect on improving childhood respiratory health.
The researchers are particularly interested in determining whether children born to mothers who took vitamin C supplements are less likely to develop asthma, which is difficult to diagnose in the first year of life.
Despite the apparent benefits of vitamin C, Dr. McEvoy said, “getting women to quit smoking during pregnancy has to be priority one.”
For those roughly 50 percent of pregnant smokers who will not, or cannot quit despite all efforts, quit smoking, vitamin C supplementation may be a simple and safe way to help their babies breathe better, she added.