title: Association between low vitamin D levels and the diagnosis of asthma in children: a systematic review of cohort studies.
abstract: BACKGROUND
  There is conflicting evidence about the association between low vitamin D levels in children and development of asthma in later life. The objective of this study was to systematically review the evidence for an epidemiological association between low serum levels of vitamin D and the diagnosis of asthma in children.
  
  
  METHODS
  We used the Cochrane methodology for conducting systematic reviews. The search strategy included an electronic search of MEDLINE and EMBASE in February 2013. Two reviewers completed, in duplicate and independently, study selection, data abstraction, and assessment of risk of bias.
  
  
  RESULTS
  Of 1081 identified citations, three cohort studies met eligibility criteria. Two studies found that low serum vitamin D level is associated with an increased risk of developing asthma late in childhood, while the third study found no association with either vitamin D2 or vitamin D3 levels. All three studies suffer from major methodological shortcomings that limit our confidence in their results.
  
  
  CONCLUSIONS
  Available epidemiological evidence suggests a potential association between low serum levels of vitamin D and the diagnosis of asthma in children. High quality studies are needed to reliably answer the question of interest.
authors: Clinical Research Institute, American University of Beirut, Beirut, Lebanon.
authors: Mhd Hashem
authors: MH
authors: Rajabbik
authors: Clinical Research Institute, American University of Beirut, Beirut, Lebanon.
authors: Tamara
authors: T
authors: Lotfi
authors: Department of Pediatrics and Adolescent Medicine, American University of Beirut, Beirut, Lebanon.
authors: Lina
authors: L
authors: Alkhaled
authors: Department of Pediatrics and Adolescent Medicine, American University of Beirut, Beirut, Lebanon.
authors: Munes
authors: M
authors: Fares
authors: Department of Internal Medicine, Calcium Metabolism and Osteoporosis Program, WHO Collaborating Center for Metabolic Bone Disorders, American University of Beirut, Beirut, Lebanon.
authors: Ghada
authors: G
authors: El-Hajj Fuleihan
authors: Department of Pediatrics and Adolescent Medicine, American University of Beirut, Beirut, Lebanon.
authors: Salman
authors: S
authors: Mroueh
authors: Clinical Research Institute, American University of Beirut, Beirut, Lebanon ; Department of Internal Medicine, Calcium Metabolism and Osteoporosis Program, WHO Collaborating Center for Metabolic Bone Disorders, American University of Beirut, Beirut, Lebanon ; Department of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, Ontario, Canada ; Department of Medicine, State University of New York at Buffalo, Buffalo, New York, USA.
authors: Elie A
authors: EA
authors: Akl
keywords: Asthma; Bronchial hyper responsiveness; Childhood; Cohort; Lung function tests; Pediatric; Systematic review; Vitamin D; Wheezing