Cooking fuels and prevalence of asthma: a global analysis of phase three of the International Study of Asthma and Allergies in Childhood (ISAAC)

Gary W K Wong, Bert Brunekreef, Philippa Ellwood, H Ross Anderson, M Innes Asher, Julian Crane, Christopher K W Lai, for the ISAAC Phase Three Study Group

Background: Indoor air pollution from a range of household cooking fuels has been implicated in the development and exacerbation of respiratory diseases. In both rich and poor countries, the effects of cooking fuels on asthma and allergies in childhood are unclear. We investigated the association between asthma and the use of a range of cooking fuels around the world.

Methods: For phase three of the International Study of Asthma and Allergies in Childhood (ISAAC), written questionnaires were self-completed at school by secondary school students aged 1314 years, 244?734 (78%) of whom were then shown a video questionnaire on wheezing symptoms. Parents of children aged 67 years completed the written questionnaire at home. We investigated the association between types of cooking fuels and symptoms of asthma using logistic regression. Adjustments were made for sex, region of the world, language, gross national income, maternal education, parental smoking, and six other subject-specific covariates. The ISAAC study is now closed, but researchers can continue to use the instruments for further research.

Results: Data were collected between 1999 and 2004. 512?707 primary and secondary school children from 108 centres in 47 countries were included in the analysis. The use of an open fire for cooking was associated with an increased risk of symptoms of asthma and reported asthma in both children aged 67 years (odds ratio [OR] for wheeze in the past year, 178, 95% CI 151210) and those aged 1314 years (OR 120, 95% CI 106137). In the final multivariate analyses, ORs for wheeze in the past year and the use of solely an open fire for cooking were 217 (95% CI 164287) for children aged 67 years and 135 (111164) for children aged 1314 years. Odds ratios for wheeze in the past year and the use of open fire in combination with other fuels for cooking were 151 (125181 for children aged 67 years and 135 (115158) for those aged 1314 years. In both age groups, we detected no evidence of an association between the use of gas as a cooking fuel and either asthma symptoms or asthma diagnosis.

Conclusions: The use of open fires for cooking is associated with an increased risk of symptoms of asthma and of asthma diagnosis in children. Because a large percentage of the world population uses open fires for cooking, this method of cooking might be an important modifiable risk factor if the association is proven to be causal.

Lancet Resp Med 2013; Epub ahead of Print


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