Children whose mothers smoked during pregnancy are at even higher risk. "We've been studying this group of children long enough that now some of them have started smoking," says lead researcher Frank Gilliland, M.D., Ph.D., professor of preventive medicine at the Keck School of Medicine of University of Southern California. "We found that teens who started smoking have a four times higher risk of developing asthma compared to teens who don't smoke. But if those same teenagers were also exposed to tobacco smoke before they were born, they get more than a double whammy - nine times the risk of getting asthma."
The researchers followed a group of 2,609 children and adolescents who were between the ages of 8 to 15 at the start of the study and had no prior history of asthma or wheezing. During the course of the study, about 28 percent of children reported smoking at any time during their life, 13.8 percent reported smoking weekly, and 6.9 percent reported smoking regularly (at least seven cigarettes per week). Children who were exposed to smoke before birth were slightly more likely to become regular smokers.
The children were tracked an average of 6.3 years, and as long as 8 years, depending on their age at joining the study and whether they continued participating. Over that time, 255 new cases of asthma were reported, with a greater percentage of girls than boys being diagnosed.
The increased risk for newly diagnosed asthma among regular, frequent smokers was largest among children who had been exposed to maternal smoking during their gestation. Children exposed in utero and who became frequent regular smokers (seven or more cigarettes per week) had an 8.8-fold increased risk compared to unexposed nonsmokers. In contrast, children who were not exposed in utero showed a small and statistically non-significant 1.2-fold increase in risk from frequent regular smoking.
MEDICA.de; Source: University of Southern California