Originally published by 2 Minute Medicine® (view original article). Reused on AccessMedicine with permission.

1. In this multi-center randomized controlled trial, vitamin C supplementation in pregnant smokers was associated with better lung function in offspring at the age of five.

2. Additionally, vitamin C supplementation in pregnant smokers was also associated with decreased occurrence of wheezing in offspring.

Evidence Rating Level: 1 (Excellent)

Exposure to cigarette smoking in utero is a risk factor for impaired fetal lung development, decreased airway function, and development of asthma in the offspring. Supplementation of vitamin C for pregnant smokers has been shown to increase offspring airway function until the age of 12 months. However, the long-term effects of vitamin C supplementation during pregnancy on airway function have not been assessed.

This multi-center randomized control trial conducted in the United States included 251 pregnant patients aged 15 years or older. Participants were current smokers, defined as having smoked ≥1 cigarette in the last week, and were between 13- and 22-weeks’ gestation. Patients were excluded if they had complex medical conditions, were currently incarcerated, or had unstable methods of communication. 125 patients were randomized to receive vitamin C (500mg/d) and 126 received placebo. The primary outcome was forced mid-expiratory flow (FEF25-75) measured by spirometry at age five. Secondary outcomes included forced expiratory volume in 1 second (FEV1) and self-reported or clinically recorded occurrence of wheeze between 4 and 6 years old.

Results demonstrated that at five years old, children of pregnant smokers who received vitamin C had improved airway function, demonstrated by improvements in FEF25-75 and significantly decreased occurrence of wheeze, compared to the placebo group. This study is limited by potential misclassification of wheeze, which was assessed using survey responses from a parent or caretaker. However, the observed clinically important improvements and lack of adverse events associated with vitamin C supplementation after a long follow-up period are high encouraging for the use of vitamin supplementation in pregnant smokers. Further trials to determine the optimal regimen and time of supplementation during initiation is still needed.

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