Effect of passive smoking on birth weight in pregnant women with vitamin D deficiency living in Turkey: A case control study

Aim: Although vitamin D deficiency in smokers has a greater risk of low birth weight than vitamin D deficiency or smoking alone, there is no study searching birth weight in vitamin D deficient passive smokers. We evaluated the effect of vitamin D deficiency on birth weight in active and passive smokers. Additionally, we aimed to determine the predictive role of vitamin D for low birth weight in smokers.

Methods: The study was designed as a retrospective case control study. A total of 210 participants were divided into three groups: active smoking (n = 34), passive smoking (n = 79), and non-smokers (n = 97). Then passive smokers were divided into two subgroups as vitamin D ≥ 20 ng/mL (n = 23) and vitamin D < 20 ng/mL (n = 56). Sociodemographic, laboratory, and perinatal characteristics were recorded and compared between groups.

Results: Birth weight was higher in non-smokers as compared to active (p < 0.001) and passive (p = 0.001) smokers, and also in passive than active smokers (p = 0.023). In passive smokers, birth weight was lower in vitamin D < 20 ng/mL group (p < 0.001). Vitamin D were correlated with birth weight in all smokers (r = 0.653, p < 0.001), passive (r = 0.624, p < 0.001) and active smokers (r = 0.526, p = 0.001). Vitamin D ≤ 14 ng/mL predicted low birth weight with 100% sensitivity and 53.92% specificity in smokers (area under curve [AUC] = 0.773, p < 0.001), with 100% sensitivity and 63.5% specificity in passive smokers (AUC = 0.759, p < 0.001) while vitamin D ≤ 11 ng/mL predicted with 83.33% sensitivity and 71.43% specificity in active smokers (AUC = 0.774, p = 0.008).

Conclusion: Vitamin D deficiency in smokers is associated with low birth weight. Although vitamin D supplementation is not routinely recommended in pregnant women, we suggest that it could be an option in preventing low birth weight in smokers, even passive ones, who do not have adequate dietary intake and have insufficient exposure to daylight.