Association between antioxidant vitamins and asthma outcomes: Systematic review and meta-analysis

Sarah Allen ¹, John Britton ¹ and Jo Leonardi-Bee ^1*

¹ University of Nottingham, United Kingdom

^* To whom correspondence should be addressed. E-mail: jo.leonardi-bee{at}nottingham.ac.uk.

Accepted 21 January 2009

Abstract

Introduction: Epidemiological studies suggest that dietary intake of vitamins A, C and E may be associated with the occurrence of asthma.

Objectives: A systematic review and meta-analysis was conducted in accordance with MOOSE guidelines to determine whether vitamins A, C, and E, measured as dietary intakes or serum levels, are associated with asthma.

Methods: We searched MEDLINE, EMBASE, CINAHL, CAB abstracts and AMED (up to November 2007), conference proceedings and bibliographies of papers to identify studies of asthma, wheeze, or airway responsiveness in relation to intakes and serum concentrations of vitamins A, C and E. Pooled odds ratios (OR) or mean differences (MD) with 95% confidence intervals (CI) were estimated, using random effects models.

Measurements and Main Results: A total of 40 studies were included. Dietary vitamin A intake was significantly lower in people with asthma compared to those without asthma (MD -182µg/day, 95% CI -288 to -75; 3 studies) and in severe compared to mild asthma (MD -344µg/day; 2 studies). Lower quantile dietary intakes (OR 1.12, 95% CI 1.04 to 1.21; 9 studies) and serum levels of vitamin C were also associated with an increased odds of asthma. Vitamin E intake was generally unrelated to asthma status but was significantly lower in severe compared to mild asthma (MD -1.20µg/day, 95% CI -2.3 to -0.1; 2 studies).

Conclusions: Relatively low dietary intakes of vitamins A and C are associated with statistically significant increased odds of asthma and wheeze. Vitamin E intake does not appear to be related to asthma status.