ASTHMA

Dietary antioxidants and asthma in adults

B D Patel^1,2, A A Welch¹, S A Bingham⁴, R N Luben¹, N E Day¹, K-T Khaw¹, D A Lomas³, N J Wareham⁵

¹ Department of Public Health and Primary Care, Institute of Public Health, Cambridge CB2 2SR, UK
² Department of Respiratory Medicine, Royal Devon and Exeter Hospital NHS Foundation Trust, Exeter EX2 5DW, UK
³ Department of Medicine, Cambridge Institute for Medical Research, Cambridge CB2 2XY, UK
⁴ MRC Dunn Nutrition Unit, Cambridge Institute for Medical Research, Cambridge CB2 2XY, UK
⁵ MRC Epidemiology Unit, Elsie Widdowson Laboratory, Cambridge CB1 9NL, UK

Correspondence to:
Dr N J Wareham
MRC Epidemiology Unit, Elsie Widdowson Laboratory, Cambridge CB1 9NL, UK; nick.wareham{at}mrc-epid.cam.ac.uk

Background: Several antioxidant nutrients have been reported to be inversely associated with asthma. A study was undertaken to assess the independent associations of these nutrients with asthma in adults.

Methods: A nested case-control study was performed in 515 adults with physician diagnosed asthma and 515 matched controls using dietary data obtained from 7 day food diaries. The main outcome measures were physician diagnosed asthma and current symptomatic asthma (diagnosed asthma and self-reported wheeze within the previous 12 months).

Results: Cases were similar to controls in age, sex, social class, and daily energy intake but had a lower median intake of fruit (132.1 v 149.1 g/day, p0.05). 51.5% of the population reported zero consumption of citrus fruit; relative to these individuals, people who consumed >46.3 g/day had a reduced risk of diagnosed and symptomatic asthma (OR adjusted for potential confounders 0.59 (95% CI 0.43 to 0.82) and 0.51 (95% CI 0.33 to 0.79), respectively). In nutrient analysis, dietary vitamin C and manganese were inversely and independently associated with symptomatic asthma (adjusted OR per quintile increase 0.88 (95% CI 0.77 to 1.00) for vitamin C and 0.85 (95% CI 0.74 to 0.98) for manganese), but only manganese was independently associated with diagnosed asthma (OR 0.86 (95% CI 0.77 to 0.95)). Adjusted plasma levels of vitamin C were significantly lower in symptomatic cases than in controls (54.3 v 58.2 µmol/l, p = 0.003).

Conclusions: Symptomatic asthma in adults is associated with a low dietary intake of fruit, the antioxidant nutrients vitamin C and manganese, and low plasma vitamin C levels. These findings suggest that diet may be a potentially modifiable risk factor for the development of asthma.

Abbreviations: BMI, body mass index; FEV₁, forced expiratory volume in 1 second; FVC, forced vital capacity; HLQ, health and lifestyle questionnaire; NRHS, Norfolk respiratory health survey

Keywords: antioxidants; asthma; diet; epidemiology

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