Change in respiratory symptom prevalence in adults who alter their smoking habits.

The prevalence of chronic cough and phlegm production has been studied in 3916 young married adults, with recent new births and young children in their families, on six consecutive annual occasions. Among those who were smokers, in all years of the study more men than women reported respiratory symptoms. Respiratory symptoms were also reported more commonly among men than among women who did not smoke at all, whereas no sex difference in symptom prevalence was apparent among men and women who changed their smoking habits during the study. Equal numbers of men stopped or started smoking on their own initiative during the second three years of the study, whereas twice as many women started smoking as stopped in the same period. Men who had been smokers in the first three years and who spontaneously stopped smoking during the second three years showed a progressive decline in respiratory symptoms to a level similar to that of nonsmokers.