Combined Effect of Air Pollution and Secondhand Smoke on Neurodevelopment at 24 Months

Abstract

Background/Aim: Neurodevelopment of infants have been associated with exposure to secondhand smoke (SHS) and air pollution (AP), respectively. There has been very few previous studies of combined effect of AP and SHS on early neurodevelopment. We aim to investigate the combined effect of AP and SHS prenatal exposure on neurodevelopment of infants at 24 months of age. Methods: We analyzed 721 mothers and their offspring from Korean multicenter birth cohort study: Mothers and Children Environmental Health (MOCEH). We measured maternal urinary cotinine to represent SHS exposure during pregnancy. Average exposure levels to PM10 (particulate matter<10in diameter) and nitrogen dioxide during the entire pregnancy were estimated using the inverse distance weighting method. Infant’s mental developmental index (MDI) and psychomotor developmental index (PDI) were measured using the Bayley Scales of Infant Development at 24 months of age. General linear model was used to assess the relationship between combined exposure of AP and SHS and neurodevelopment. Results: MDI score of 24 months aged infants was associated with cotinine [β= -2.56, 95%confidence interval (CI): -4.58, -0.53] in mothers with early pregnancy urinary cotinine levels >1.90 ng/ml. The MDI score of infant was more decreased in mothers exposed to both PM10 >50 mg/m3 during pregnancy and high exposure of SHS [β= -2.85, 95%CI: -5.17, -0.54]. The negative association was reduced when children received breast milk up to 6 months [β= 0.06, 95%CI: -3.13, 3.24]. However, the combined effect was more pronounced in mothers with both GSTM1/GSTT1 null type on MDI [β= -8.17, 95%CI: -12.27, -4.06] and PDI [β= -3.65, 95% CI: -7.38, 0.08]. Conclusions: These findings suggest that maternal combined exposure to PM10 and SHS during pregnancy may result in delayed neurodevelopment in early childhood and propose its combined effects. The effect might be modified by genetic polymorphism and breastfeeding.