Longitudinal study of parental smoking habits and development of asthma in early childhood

Abstract Objective This study examined the association between parental smoking habits and the development of asthma in early childhood by using representative samples. Methods The survey subjects included all of the 53,575 babies born in Japan during the periods January 10–17 and July 10–17, 2001. The families of the subjects were asked to complete questionnaires that were delivered by post at 6 months, 1 year 6 months, 2 years 6 months, 3 years 6 months, and 4 years 6 months postpartum. The first survey contained questions regarding the smoking habits of the parents. The second to fifth surveys asked if the child had needed medical attention for the treatment of asthma. Results Data from 36,888 subjects (collection rate: 68.9%) were analyzed. The 4-year cumulative incidence of asthma was 12.0%. Maternal indoor smoking significantly increased the risk of asthma development in children, 4-year risk 14.4% vs. 11.7%, risk ratio = 1.24, 95% CI: 1.11 to 1.38. No statistically significant association was found between paternal smoking and asthma development in children. Conclusions In order to prevent the development of asthma in early childhood, it is necessary to formulate measures to stop or discourage maternal smoking.