title: Observational studies on the effect of dietary antioxidants on asthma: a meta-analysis.
abstract: OBJECTIVE
  It has been suggested that the rapid increase in asthma prevalence may in part be due to a decrease in the intake of dietary antioxidants, including vitamin C, vitamin E and beta-carotene. Epidemiological studies investigating the association between dietary antioxidant intake and asthma have generated inconsistent results. A meta-analysis was undertaken to examine the association between dietary antioxidant intake and the risk of asthma.
  
  
  METHODS
  The MEDLINE database was searched for observational studies in English-language journals from 1966 to March 2007. Data were extracted using standardized forms. Pooled odds ratios (OR) with 95% confidence intervals (CI) were calculated using a random effects model. Ten studies were eligible for inclusion. Seven studies, comprising 13 653 subjects, used asthma or wheeze as their outcome; three studies explored the effect of antioxidant intake on lung function.
  
  
  RESULTS
  A higher dietary intake of antioxidants was not associated with a lower risk of having asthma. The pooled OR for having asthma were 1.06 (95% CI: 0.79-1.43) for subjects with a higher dietary vitamin C intake compared with those with a lower intake; 0.88 (95% CI: 0.61-1.25) for vitamin E; and 1.12 (95% CI: 0.77-1.62) for beta-carotene. There was no significant association between dietary antioxidant intake and lung function except for a positive association between vitamin C intake and an increase in FEV(1) (29.1 mL, 95% CI: -0.4-58.6, P = 0.05).
  
  
  CONCLUSIONS
  This meta-analysis does not support the hypothesis that dietary intake of the antioxidants vitamins C and E and beta-carotene influences the risk of asthma.
authors.affiliation: Department of Respiratory Diseases, Peking Union Medical College Hospital, Peking Union Medical College and Chinese Academy of Medical Sciences, Beijing, China. gaojm@pumch.cn
authors.forename: Jinming
authors.initials: J
authors.lastname: Gao
authors.forename: Xiang
authors.initials: X
authors.lastname: Gao
authors.forename: Weijuan
authors.initials: W
authors.lastname: Li
authors.forename: Yuanjue
authors.initials: Y
authors.lastname: Zhu
authors.forename: Philip J
authors.initials: PJ
authors.lastname: Thompson
mesh_terms: D000975:Antioxidants / Q000008:administration & dosage*; D001205:Ascorbic Acid / Q000008:administration & dosage; D001249:Asthma / Q000453:epidemiology*; D003430:Cross-Sectional Studies; D004032:Diet; D004435:Eating; D006801:Humans; D016017:Odds Ratio; D014810:Vitamin E / Q000008:administration & dosage; D019207:beta Carotene / Q000008:administration & dosage
chemical_list: D000975:Antioxidants; D019207:beta Carotene; D014810:Vitamin E; D001205:Ascorbic Acid