Children and teenagers who smoke regularly have been found to have an almost four times greater risk of developing asthma compared with nonsmokers.
Researchers from the University of Southern California at Los Angeles studied more than 2,600 children with no history of asthma or wheezing. The children were recruited from fourth- and seventh-grade classrooms and ranged in age from eight to 15 years.
Those who smoked seven or more cigarettes per week on average and 300 or more cigarettes in the year prior to an annual physical were considered regular smokers.
Just over 250 new cases of asthma were diagnosed during the followup period, which was six years for the fourth-grade students and four years for the seventh-grade students.
Adolescents who were classified as regular smokers on a yearly basis were found to have a 3.9-fold increased risk of developing asthma compared with those who reported not smoking in the previous year.
Other factors, such as maternal smoking habits and a lack of allergies, were also associated with higher rates of asthma.
Those who smoked regularly and who had been exposed to maternal smoking in the womb had an 8.8-times greater risk of developing asthma compared with nonsmokers who had not been exposed to maternal smoking.
Regular smokers who did not have allergies also had a five-times greater risk of developing asthma than nonsmoking, non-allergic study participants.
The study researchers concluded that efforts to prevent smoking among children, adolescents and women of childbearing age are imperative to reducing the number of preventable asthma cases.