Background Exposure to parental smoking is associated with wheeze in early childhood, but in 2006 the US Surgeon General stated that the evidence is insufficient to infer a causal relationship between exposure and asthma in childhood and adolescents.
Aims To examine the association between maternal and paternal smoking and symptoms of asthma, eczema and rhinoconjunctivitis.
Methods Parents or guardians of children aged 6–7 years completed written questionnaires about symptoms of asthma, rhinoconjunctivitis and eczema, and several risk factors, including maternal smoking in the child's first year of life, current maternal smoking (and amount) and paternal smoking. Adolescents aged 13–14 years self completed the questionnaires on these symptoms and whether their parents currently smoked.
Results In the 6–7-year age group there were 220 407 children from 75 centres in 32 countries. In the 13–14-year age group there were 350 654 adolescents from 118 centres in 53 countries. Maternal and paternal smoking was associated with an increased risk of symptoms of asthma, eczema and rhinoconjunctivitis in both age groups, although the magnitude of the OR is higher for symptoms of asthma than the other outcomes. Maternal smoking is associated with higher ORs than paternal smoking. For asthma symptoms there is a clear dose relationship (1–9 cigarettes/day, OR 1.27; 10–19 cigarettes/day, OR 1.35; and 20+ cigarettes/day, OR 1.56). When maternal smoking in the child's first year of life and current maternal smoking are considered, the main effect is due to maternal smoking in the child's first year of life. There was no interaction between maternal and paternal smoking.
Conclusions This study has confirmed the importance of maternal smoking, and the separate and additional effect of paternal smoking. The presence of a dose–response effect relationship with asthma symptoms suggests that the relationship is causal, however for eczema and rhinoconjunctivitis causality is less certain.
- environmental tobacco smoke exposure
- asthma epidemiology
- tobacco and the lung
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Funding Currently the main source of funding for the ISAAC International Data Centre (IIDC) is The New Zealand Lotteries Grant Board. Many New Zealand funding bodies have contributed support for the IIDC during the periods of fieldwork and data compilation (the Health Research Council of New Zealand, the Asthma and Respiratory Foundation of New Zealand, the Child Health Research Foundation, the Hawke's Bay Medical Research Foundation, the Waikato Medical Research Foundation, The Auckland Medical Research Foundation, Glaxo Wellcome New Zealand and Astra Zeneca New Zealand). Glaxo Wellcome International Medical Affairs and The BUPA Foundation supported the regional coordination for Phase Three and the IIDC. Without help from all of the above, ISAAC would not have been such a global success. EA Mitchell is supported by Cure Kids (NZ).
Competing interests None.
Ethics approval Each participating centres obtained approval according to their laws and regulations.
Provenance and peer review Not commissioned; externally peer reviewed.
Data sharing statement At this moment in time the data are confidential to each centre and the ISAAC International Data Centre.
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