title: Association between vitamin D and respiratory outcomes in Canadian adolescents and adults.
abstract: BACKGROUND
  Asthma is one of the most prevalent chronic diseases worldwide, affecting more than 200 million people. Vitamin D deficiency has been reported among individuals with asthma and might play a role in asthma exacerbations. In this cross-sectional study, we investigated the association of serum 25-hydroxy vitamin D [25(OH)D] levels and current asthma, ever asthma, and lung function.
  
  
  METHODS
  Data from 3937 subjects aged 13-69 years who participated in the Canadian Health Measures Survey - Cycle 1 were considered in this study. Serum 25(OH)D levels were categorized into ≤49 nmol/L (low), 50-74 nmol/L (moderate) and ≥75 nmol/L (high).
  
  
  RESULTS
  The proportion of subjects with current and ever asthma was greater in the lower 25(OH)D category than in moderate and high categories. After adjusting for potential confounders, subjects in the low 25(OH)D levels were more likely to have current asthma than those in the moderate levels (OR: 1.54, 95% CI: 1.01-2.36). Low 25(OH)D levels were also associated with ever asthma (OR: 2.12, 95% CI: 1.40-3.21) among those with a family history of asthma and this association was stronger in those with asthma onset before 20 years of age. High 25(OH)D levels were associated with lower mean value of FEV1/FVC ratio. No significant association was observed between 25(OH)D levels and other lung function measurements.
  
  
  CONCLUSIONS
  In this study, 25(OH)D levels below 50 nmol/L were associated with an increased risk of current and ever asthma. Further exploration of this relationship is needed to determine the optimal level of vitamin D in the management of asthma in adolescents and adults.
authors.affiliation: a School of Public Health, University of Alberta, Edmonton , Alberta , Canada and.
authors.forename: Selvanayagam John
authors.initials: SJ
authors.lastname: Niruban
authors.forename: Kannayiram
authors.initials: K
authors.lastname: Alagiakrishnan
authors.forename: Jeremy
authors.initials: J
authors.lastname: Beach
authors.forename: Ambikaipakan
authors.initials: A
authors.lastname: Senthilselvan
mesh_terms: D000293:Adolescent; D000328:Adult; D017668:Age of Onset; D000368:Aged; D001249:Asthma / Q000097:blood* / Q000150:complications*; D002170:Canada / Q000453:epidemiology; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012129:Respiratory Function Tests; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood; D014808:Vitamin D Deficiency / Q000097:blood* / Q000150:complications*
chemical_list: D014807:Vitamin D; C104450:25-hydroxyvitamin D
keywords: Asthma; family history; lung function; serum 25-hydroxy vitamin D