The ecological relationship of tobacco smoking to the prevalence of symptoms of asthma and other atopic diseases in children: the International Study of Asthma and Allergies in Childhood (ISAAC)

This study examined the relationship between parental smoking and asthma and other atopic diseases at the ecological level. The prevalence of atopic symptoms in 6–7- and 13–14-year old children was assessed in 91 centres (from 38 countries) and 155 centres (from 56 countries) respectively in the International Study of Asthma and Allergy in Childhood (ISAAC). These symptoms were related to prevalence of tobacco smoking for each country by gender as reported by the World Health Organisation. There was a significant negative association between the prevalence of smoking by men and the prevalence of symptoms of asthma and rhinitis, but not eczema in the 13–14-year age group. There was a significant positive relationship between prevalence of smoking by women and prevalence of wheeze in the last 12 months, but not for any other symptoms in the 13–14-year age group. In the 6–7-year age group, there was a significant negative correlation between prevalence of smoking by men and the prevalence of wheeze causing sleep disturbance and a close to significant negative association at the 5% level with the prevalence of wheeze in the last 12 months and rhinitis. Thus, for the countries that are included in this analysis, countries that have high adult male smoking rates have a lower risk of asthma and rhinitis symptoms in children. It should be stressed that this analysis does not involve information on individual exposures and therefore does not contradict the well-established association of active and passive smoking in individuals with the occurrence of asthma symptoms in the same individuals. Rather, it indicates that this well-established individual-level association does not account for the international differences in asthma prevalence, and that other risk factors for asthma must be responsible for the observed international patterns.