title: In utero exposure to 25-hydroxyvitamin D and risk of childhood asthma, wheeze, and respiratory tract infections: A meta-analysis of birth cohort studies.
abstract: BACKGROUND
  Studies of the associations between in utero 25-hydroxyvitamin D (25[OH]D) exposure and risk of childhood asthma, wheeze, and respiratory tract infections are inconsistent and inconclusive.
  
  
  OBJECTIVE
  We sought to assess associations between 25(OH)D levels in cord blood or maternal venous blood and risk of offspring's asthma, wheeze, and respiratory tract infections.
  
  
  METHODS
  Data were derived from PubMed, Embase, Google Scholar, references from relevant articles, and de novo results from published studies until December 2015. A random-effects meta-analysis was conducted among 16 birth cohort studies.
  
  
  RESULTS
  Comparing the highest with the lowest category of 25(OH)D levels, the pooled odds ratios were 0.84 (95% CI, 0.70-1.01; P = .064) for asthma, 0.77 (95% CI, 0.58-1.03; P = .083) for wheeze, and 0.85 (95% CI, 0.66-1.09; P = .187) for respiratory tract infections. The observed inverse association for wheeze was more pronounced and became statistically significant in the studies that measured 25(OH)D levels in cord blood (0.43; 95% CI, 0.29-0.62; P < .001).
  
  
  CONCLUSIONS
  Accumulated evidence generated from this meta-analysis suggests that increased in utero exposure to 25(OH)D is inversely associated with the risk of asthma and wheeze during childhood. These findings are in keeping with the results of 2 recently published randomized clinical trials of vitamin D supplementation during pregnancy.
authors.affiliation: Department of Clinical Nutrition, Ren Ji Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai, China.
authors.forename: Haixia
authors.initials: H
authors.lastname: Feng
authors.affiliation: Department of Epidemiology and Biostatistics, School of Public Health-Bloomington, Indiana University, Bloomington, Ind.
authors.forename: Pengcheng
authors.initials: P
authors.lastname: Xun
authors.affiliation: Respiratory, Critical Care and Anaesthesia, UCL Institute of Child Health, London, United Kingdom.
authors.forename: Katharine
authors.initials: K
authors.lastname: Pike
authors.affiliation: School of Clinical Sciences, University of Bristol, Bristol, United Kingdom.
authors.forename: Andrew K
authors.initials: AK
authors.lastname: Wills
authors.affiliation: Copenhagen Prospective Studies on Asthma in Childhood (COPSAC), Herlev and Gentofte Hospital, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Bo L
authors.initials: BL
authors.lastname: Chawes
authors.affiliation: Copenhagen Prospective Studies on Asthma in Childhood (COPSAC), Herlev and Gentofte Hospital, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Hans
authors.initials: H
authors.lastname: Bisgaard
authors.affiliation: Department of Clinical Nutrition, Xin Hua Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai, China; Shanghai Key Laboratory of Pediatric Gastroenterology and Nutrition, and the Shanghai Institute of Pediatric Research, Shanghai, China; Department of Pediatric Surgery, Xin Hua Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai, China.
authors.forename: Wei
authors.initials: W
authors.lastname: Cai
authors.affiliation: Department of Clinical Nutrition, Ren Ji Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai, China. Electronic address: wanyp204@163.com.
authors.forename: Yanping
authors.initials: Y
authors.lastname: Wan
authors.affiliation: Department of Epidemiology and Biostatistics, School of Public Health-Bloomington, Indiana University, Bloomington, Ind. Electronic address: kahe@indiana.edu.
authors.forename: Ka
authors.initials: K
authors.lastname: He
mesh_terms: D001249:Asthma / Q000453:epidemiology*; D002675:Child, Preschool; D015331:Cohort Studies; D019587:Dietary Supplements; D005260:Female; D005312:Fetal Blood / Q000737:chemistry; D006801:Humans; D008297:Male; D008431:Maternal-Fetal Exchange; D016017:Odds Ratio; D011247:Pregnancy / Q000097:blood; D012135:Respiratory Sounds; D012141:Respiratory Tract Infections / Q000453:epidemiology*; D012306:Risk; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood
chemical_list: D014807:Vitamin D; C104450:25-hydroxyvitamin D
keywords: 25(OH)D; asthma; birth cohort studies; meta-analysis; respiratory tract infections; wheeze