title: Nutrients and foods for the primary prevention of asthma and allergy: systematic review and meta-analysis.
abstract: BACKGROUND
  Epidemiologic studies suggest that deficiencies of the nutrients selenium; zinc; vitamins A, C, D, and E; and low fruit and vegetable intake may be associated with the development of asthma and allergic disorders.
  
  
  OBJECTIVE
  To investigate the evidence that nutrient and food intake modifies the risk of children developing allergy.
  
  
  METHODS
  We systematically searched 11 databases. Studies were critically appraised, and meta-analyses were undertaken.
  
  
  RESULTS
  We identified 62 eligible reports. There were no randomized controlled trials. Studies used cohort (n = 21), case-control (n = 15), or cross-sectional (n = 26) designs. All studies were judged to be at moderate to substantial risk of bias. Meta-analysis revealed that serum vitamin A was lower in children with asthma compared with controls (odds ratio [OR], 0.25; 95% CI, 0.10-0.40). Meta-analyses also showed that high maternal dietary vitamin D and E intakes during pregnancy were protective for the development of wheezing outcomes (OR, 0.56, 95% CI, 0.42-0.73; and OR, 0.68, 95% CI, 0.52-0.88, respectively). Adherence to a Mediterranean diet was protective for persistent wheeze (OR, 0.22; 95% CI, 0.08-0.58) and atopy (OR, 0.55; 95% CI, 0.31-0.97). Seventeen of 22 fruit and vegetable studies reported beneficial associations with asthma and allergic outcomes. Results were not supportive for other allergic outcomes for these vitamins or nutrients, or for any outcomes in relation to vitamin C and selenium.
  
  
  CONCLUSIONS
  The available epidemiologic evidence is weak but nonetheless supportive with respect to vitamins A, D, and E; zinc; fruits and vegetables; and a Mediterranean diet for the prevention of asthma. Experimental studies of these exposures are now warranted.
authors.affiliation: Allergy and Respiratory Research Group Centre for Population Health Sciences, University of Edinburgh, Medical School, Edinburgh, United Kingdom.
authors.forename: Ulugbek
authors.initials: U
authors.lastname: Nurmatov
authors.forename: Graham
authors.initials: G
authors.lastname: Devereux
authors.forename: Aziz
authors.initials: A
authors.lastname: Sheikh
mesh_terms: D001249:Asthma / Q000517:prevention & control*; D001361:Avitaminosis; D002648:Child; D004032:Diet; D005260:Female; D005638:Fruit; D006801:Humans; D009747:Nutritional Physiological Phenomena / Q000276:immunology*; D011247:Pregnancy; D014675:Vegetables; D014801:Vitamin A; D014807:Vitamin D
chemical_list: D014801:Vitamin A; D014807:Vitamin D