Effects of cigarette smoking on lung function in adolescent boys and girls

Background: Little is known about the sex-specific effects of cigarette smoking on the level and growth of lung function in adolescence, when 71 percent of people in the United States who smoke tried their first cigarette. Methods: We studied the effects of cigarette smoking on the level and rate of growth of pulmonary function in a cohort of 5158 boys and 4902 girls 10 to 18 years of age, examined annually between 1974 and 1989 in six cities in the United States. Results: We found a dose-response relation between smoking and lower levels of both the ratio of forced expiratory volume in one second to forced vital capacity (FEV₁/FVC) and the forced expiratory flow between 25 and 75 percent of FVC (FEF_{25 -75}). Each pack per day of smoking was associated with a 3.2 percent reduction in FEF_25-75 for girls (P=0.01) and a 3.5 percent reduction in FEF_25-75 for boys (P=0.007). Whereas the FVC level was elevated in smokers, the rate of growth of FVC and FEV₁, was reduced. Among adolescents of the same sex, smoking five or more cigarettes a day, as compared with never smoking, was associated with 1.09 percent slower growth of FEV₁ per year in girls (95 percent confidence interval, 0.70 to 1.47 percent) and 0.20 percent slower growth in boys (95 percent confidence interval, -0.16 to 0.56 percent), and with 1.25 percent slower growth of FEF_25-75 per year in girls (95 percent confidence interval, 0.38 to 2.13 percent) and 0.93 percent slower growth in boys (95 percent confidence interval, 0.21 to 1.65 percent). Whereas girls who did not smoke reached a plateau in lung function at 17 to 18 years of age, girls of the same age who smoked had a decline of FEV₁ and FEF_25-75. Conclusions: Cigarette smoking is associated with evidence of mild airway obstruction and slowed growth of lung function in adolescents. Adolescent girls may be more vulnerable than boys to the effects of smoking on the growth of lung function.