While its best to quit smoking during pregnancy, for women who cannot, taking vitamin C supplements can reduce their babies' risk of developing a wheeze, finds a study.

Wheeze is a condition of producing whistle like sound due to obstructed lower respiratory tract. The results showed statistically significant difference in lung function between the babies, at three months of age, born to women who took supplemental vitamin C every day and those who were prescribed a placebo. Despite the apparent benefits of vitamin C, "getting women to quit smoking during pregnancy has to be priority one", said lead author Cynthia McEvoy, of Oregon Health & Science University (OHSU), US.

For those roughly 50 per cent 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. Previous study revealed that daily supplemental vitamin C in pregnant women who could not quit smoking reduced the harm on babies's lungs.

Vitamin C 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", said Eliot Spindel from the varsity. It can also "prevent some of the epigenetic changes that contribute to the lifelong effects of in-utero tobacco exposure," Spindel noted.

In the study, presented during American Thoracic Society International Conference at San Diego, the team measured the force expiratory flows (FEFs) -- speed with which air can be forced out of the lung - among babies. The mothers were divided into two groups and were administered 500 mg of supplemental vitamin C every day and a placebo in addition to the same prenatal vitamin accordingly.