Exposure to environmental tobacco smoke (ETS) in the womb increased the rate of physician-diagnosed asthma in young persons while current ETS exposure was associated with wheezing but not with physician-diagnosed asthma.
Researchers who studied 5,762 school-aged children residing in 12 Southern California communities made this significant finding.
Writing in the February issue of the American Journal of Respiratory and Critical Care Medicine, Frank D. Gilliland, M.D.,Ph.D., and two associates from the Department of Preventive Medicine, Keck School of Medicine, University of Southern California, Los Angeles, studied responses to a self-administered questionnaire completed by the parents of 4th, 7th, and 10th grade students to ascertain which children either wheezed or had physician-diagnosed asthma.
In the United States, an estimated 15 million children, accounting for more than 25 percent of the population in this age group, are currently exposed to household ETS and are at risk for adverse health effects from this exposure, according to the researchers.
"A substantial body of evidence indicates that involuntary exposure to tobacco smoke adversely affects children's respiratory health," said Dr. Gilliland. "It can lead to decreased lung growth and increase the risk of respiratory infections, including wheezing and exacerbation of asthma."
The 5,267 children who participated in the research were involved in the Children's Health Study, a 10-year longitudinal investigation of the effects of air pollution on children's respiratory health.
The investigators used lifetime tobacco smoke exposure histories and parental reports of wheezing and physician-diagnosed asthma to examine the relationship of maternal smoking during pregnancy and childhood exposure to ETS to the development of wheezing or asthma.
The majority of students were 10 years of age or younger, white, and from households with health insurance and high educational attainment. Exposure in the womb occurred in 18.8 percent of the children, with 39.5 percent incurring some lifetime exposure to ETS.
According to the article, the lifetime prevalence of wheezing among these children was 33.7 percent, with physician-diagnosed asthma being reported by 14.6 percent.
Current ETS exposure was associated with an increased prevalence of a wider range of wheezing subcategories. This included wheezing with or without colds, attacks of wheezing with shortness of breath or nighttime awakening, wheezing with exercise, and wheeze requiring medication or emergency care.
Neither previous nor current ETS exposure was significantly associated with active asthma, asthma requiring medication, or persistent wheezing. However, the prevalence of two or more household smokers was associated with all subcategories of wheezing.
In remarking about the public health significance of their findings, the investigators estimated that the elimination of in utero exposure of fetuses to maternal smoking would prevent 5 to 15 percent of asthma cases in children.
They said that to reduce the burden of chronic respiratory disease on children, physicians, partners, and relatives should encourage women of childbearing age to stop smoking.