title: Antibiotic treatment during infancy and increased body mass index in boys: an international cross-sectional study.
abstract: OBJECTIVE
  To investigate whether antibiotic exposure during the first year of life is associated with increased childhood body mass index (BMI).
  
  
  METHODS
  Secondary analysis from a multi-centre, multi-country, cross-sectional study (The International Study of Asthma and Allergies in Childhood Phase Three).
  
  
  METHODS
  A total of 74 946 children from 31 centres in 18 countries contributed data on antibiotic use in the first 12 months of life and current BMI.
  
  
  METHODS
  Parents/guardians of children aged 5-8 years completed questionnaires that included questions about their children's current height and weight, and whether in the child's first 12 months of life, they had received any antibiotics, paracetamol, were breastfed or the mother/female guardian smoked cigarettes, and whether the child had wheezed in the past 12 months. A general linear mixed model was used to determine the association of antibiotic exposure with BMI, adjusting for age, sex, centre, BMI measurement type (self-reported or measured), maternal smoking, breastfeeding, paracetamol use, gross national income and current wheeze.
  
  
  RESULTS
  There was a significant interaction between sex and early-life antibiotic exposure. Early-life antibiotic exposure was associated with increased childhood BMI in boys (+0.107 kg m(-2), P<0.0001), but not in girls (-0.008 kg m(-2), P=0.75) after controlling for age, centre and BMI measurement type. The association remained in boys (+0.104 kg m(-2), P<0.0007), after adjustment for maternal smoking, breastfeeding, paracetamol use and current wheeze. There was no interaction between age, maternal smoking, breastfeeding, paracetamol use, gross national income and current wheeze in the association between early antibiotic exposure and BMI.
  
  
  CONCLUSIONS
  Exposure to antibiotics during the first 12 months of life is associated with a small increase in BMI in boys aged 5-8 years in this large international cross-sectional survey. By inference this provides additional support for the importance of gut microbiota in modulating the risk of obesity, with a sex-specific effect.
authors.affiliation: Department of Medicine, Faculty of Medical and Health Sciences, The University of Auckland, Auckland, New Zealand.
authors.forename: R
authors.initials: R
authors.lastname: Murphy
authors.affiliation: School of Population Health, Faculty of Medical and Health Sciences, The University of Auckland, Auckland, New Zealand.
authors.forename: A W
authors.initials: AW
authors.lastname: Stewart
authors.affiliation: Medical Research Institute of New Zealand, Newtown, New Zealand.
authors.forename: I
authors.initials: I
authors.lastname: Braithwaite
authors.affiliation: Medical Research Institute of New Zealand, Newtown, New Zealand.
authors.forename: R
authors.initials: R
authors.lastname: Beasley
authors.affiliation: Department of Preventive and Social Medicine, Dunedin School of Medicine, University of Otago, Otago, New Zealand.
authors.forename: R J
authors.initials: RJ
authors.lastname: Hancox
authors.affiliation: Department of Paediatrics: Child and Youth Health, Faculty of Medical and Health Sciences, The University of Auckland, Auckland, New Zealand.
authors.forename: E A
authors.initials: EA
authors.lastname: Mitchell
mesh_terms: D000082:Acetaminophen / Q000008:administration & dosage / Q000009:adverse effects*; D000900:Anti-Bacterial Agents / Q000008:administration & dosage / Q000009:adverse effects*; D001249:Asthma / Q000139:chemically induced / Q000453:epidemiology / Q000276:immunology*; D015992:Body Mass Index; D001942:Breast Feeding / Q000706:statistics & numerical data; D002648:Child; D002675:Child, Preschool; D003430:Cross-Sectional Studies; D005260:Female; D065569:Gastrointestinal Absorption / Q000276:immunology*; D006801:Humans; D008297:Male; D015337:Multicenter Studies as Topic; D010290:Parents; D015995:Prevalence; D012307:Risk Factors; D012737:Sex Factors; D012907:Smoking / Q000009:adverse effects* / Q000276:immunology; D012959:Socioeconomic Factors; D011795:Surveys and Questionnaires
chemical_list: D000900:Anti-Bacterial Agents; D000082:Acetaminophen