title: Early life exposure to ambient air pollution and childhood asthma in China.
abstract: BACKGROUND
  Early life is suggested to be a critical time in determining subsequent asthma development, but the extent to which the effect of early-life exposure to ambient air pollution on childhood asthma is unclear.
  
  
  OBJECTIVE
  We investigated doctor-diagnosed asthma in preschool children due to exposure to ambient air pollution in utero and during the first year of life.
  
  
  METHODS
  In total 2490 children aged 3-6 years participated in a questionnaire study regarding doctor-diagnosed asthma between September 2011 and January 2012 in China. Children's exposure to critical air pollutants, sulfur dioxide (SO2) as proxy of industrial air pollution, nitrogen dioxide (NO2) as proxy of traffic pollution, and particulate matter≤10µm in diameter (PM10) as a mixture, was estimated from the concentrations measured at the ambient air quality monitoring stations by using an inverse distance weighted (IDW) method. Logistic regression analysis was employed to determine the relationship between early-life exposure and childhood asthma in terms of odds ratio (OR) and 95% confidence interval (CI).
  
  
  RESULTS
  Association between early-life exposure to air pollutants and childhood asthma was observed. SO2 and NO2 had significant associations with adjusted OR (95% CI) of 1.45 (1.02-2.07) and 1.74 (1.15-2.62) in utero and 1.62 (1.01-2.60) and 1.90 (1.20-3.00) during the first year for per 50 µg/m(3) and 15 µg/m(3) increase respectively. Exposure to the combined high level of SO2 and NO2 in China significantly elevated the asthmatic risk with adjusted OR (95% CI) of 1.76 (1.18-2.64) in utero and 1.85 (1.22-2.79) during the first year compared to the low level exposure. The associations were higher for males and the younger children aged 3-4 than females and the older children aged 5-6.
  
  
  CONCLUSIONS
  Early-life exposure to ambient air pollution is associated with childhood asthma during which the level and source of air pollution play important roles. The high level and nature of combined industrial and traffic air pollution in China may contribute to the recent rapid increase of childhood asthma.
authors.affiliation: School of Energy Science and Engineering, Central South University, Changsha, China; Institute of Environmental Health, Central South University, Changsha, China. Electronic address: qhdeng@csu.edu.cn.
authors.forename: Qihong
authors.initials: Q
authors.lastname: Deng
authors.affiliation: School of Energy Science and Engineering, Central South University, Changsha, China.
authors.forename: Chan
authors.initials: C
authors.lastname: Lu
authors.affiliation: Department of Medical Sciences/Occupational & Environmental Medicine, Uppsala University, Uppsala, Sweden.
authors.forename: Dan
authors.initials: D
authors.lastname: Norbäck
authors.affiliation: Department of Public Health Sciences, Karlstad University, Karlstad, Sweden.
authors.forename: Carl-Gustaf
authors.initials: CG
authors.lastname: Bornehag
authors.affiliation: School of Architecture, Tsinghua University, Beijing, China.
authors.forename: Yinping
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: School of Energy Science and Engineering, Central South University, Changsha, China; Institute of Environmental Health, Central South University, Changsha, China.
authors.forename: Weiwei
authors.initials: W
authors.lastname: Liu
authors.affiliation: Institute of Environmental Health, Central South University, Changsha, China; The Third Xiangya Hospital, Central South University, Changsha, China.
authors.forename: Hong
authors.initials: H
authors.lastname: Yuan
authors.affiliation: School of Energy Science and Engineering, Central South University, Changsha, China; School of Architecture, Tsinghua University, Beijing, China.
authors.forename: Jan
authors.initials: J
authors.lastname: Sundell
mesh_terms: D000393:Air Pollutants / Q000009:adverse effects / Q000032:analysis*; D001249:Asthma / Q000139:chemically induced / Q000453:epidemiology*; D002648:Child; D002675:Child, Preschool; D002681:China / Q000453:epidemiology; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D019570:Inhalation Exposure / Q000009:adverse effects / Q000032:analysis*; D008297:Male; D052638:Particulate Matter / Q000009:adverse effects / Q000032:analysis*; D011247:Pregnancy; D011297:Prenatal Exposure Delayed Effects / Q000139:chemically induced / Q000453:epidemiology*; D011795:Surveys and Questionnaires
chemical_list: D000393:Air Pollutants; D052638:Particulate Matter
keywords: Asthma; Children; First year of life; In utero; Nitrogen dioxide; Particulate matter; Pregnancy; Sulfur dioxide