Observational studies on the effect of dietary antioxidants on asthma: a meta-analysis

Respirology. 2008 Jun;13(4):528-36. doi: 10.1111/j.1440-1843.2008.01286.x. Epub 2008 Apr 10.


Background and 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.

Publication types

  • Meta-Analysis
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antioxidants / administration & dosage*
  • Ascorbic Acid / administration & dosage
  • Asthma / epidemiology*
  • Cross-Sectional Studies
  • Diet*
  • Eating
  • Humans
  • Odds Ratio
  • Vitamin E / administration & dosage
  • beta Carotene / administration & dosage


  • Antioxidants
  • beta Carotene
  • Vitamin E
  • Ascorbic Acid