Regular smoking substantially increases risk of asthma in adolescents

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Frank D. Gilliland, M.D., Ph.D., of the Keck School of Medicine at the University of Southern California, and six associates analyzed 2,609 children with no prior history of either asthma or wheezing. All participants were recruited from fourth- and seventh-grade classrooms in 12 southern California communities as part of the CHS, which tracked the respiratory health of school-aged children during the 1990s.

For periods of five to eight years (depending on a student's age at the beginning of the study), the investigators annually collected data on demographic factors, medical histories, household exposures, cigarette smoking and newly diagnosed asthma through interviews and questionnaires. They used this information to estimate a child's relative risk for new-onset asthma.

"The results of our study provide clear evidence that regular smoking increases the risk for asthma and that important chronic adverse consequences of smoking are not restricted to individuals who have smoked for many years," said Dr. Gilliland.

Among the children studied, there were 255 cases of new onset asthma (104 males and 151 females). Children who reported smoking 300 or more cigarettes per year had almost a four-fold increased risk for new-onset asthma compared with nonsmokers. Surprisingly, this increased risk was greater in non-allergic children than those with a history of allergies.

The adolescents most at risk for developing asthma, Dr. Gilliland noted, are those who were exposed to cigarette smoke while in the womb and who later became regular smokers (seven or more cigarettes per day). The investigators found this combination led to more than an eight-fold increased risk of asthma compared with unexposed nonsmokers.

"The effects of smoking may be mediated by changes in airway function, as smoking causes increased bronchial hyper-responsiveness in children and adults without asthma," said Dr. Gilliland. "The combined effect of increased bronchial hyper-responsiveness and the pro-inflammatory milieu in smokers may set the stage for the onset of asthma."

The link between active smoking with asthma were not substantially affected by adjustments for demographic factors like educational attainment, family income, birth weight, gestational age, health insurance availability, physical activity levels, family history of asthma, pets, humidifier use, other household characteristics, or exposure to ambient pollutants and indoor combustion sources, including secondhand smoke.

"The clinical and public health implications of our findings are far-reaching," said Dr. Gilliland. "Effective tobacco control efforts focusing on the prevention of smoking in children, adolescents and women of childbearing age are urgently needed to reduce the number of these preventable cases of asthma."

American Thoracic Society