Smoking exposure trajectories and pulmonary function in early adulthood in a Brazilian cohort.

Objectives: To investigate smoking trajectories and their association with pulmonary function (PF) and respiratory symptoms at age 22.

Methods: Data from a population-based cohort study of 3350 individuals and their spirometries were analysed. The outcomes were: forced expiratory volume in the first second (FEV₁), forced vital capacity (FVC), forced expiratory flow at the mid expiratory phase (FEF_25-75 %), FEV₁/FVC and FEF_25-75/FVC ratio. Smoking data were collected at perinatal follow-up (gestational exposure) and 15, 18 and 22 years. Group-based trajectory model was applied.

Results: Four groups were identified: no exposure (NE), gestational (GE), gestational and adulthood (GAE) and continuous (CE) exposure. Both CE and GAE trajectories were associated with lower values of FEV₁/FVC (-1.77pp; p = 0.01 and -1.58 pp; p<0.001 respectively) and FEF_25-75/FVC ratio (-7.27pp; p = 0.019 and -6.04pp; p<0.001 respectively) compared to the NE trajectory. Lower FEV₁ and FEF_25-75 % values were also related to the GAE trajectory (-68 ml; p = 0.03 and -253 ml/s_; p<0.001 respectively). Compared to those who never smoked, individuals who smoked 10 or more cigarettes daily presented a reduction in the FEV₁/FVC ratio by 1.37pp (p<0.001), FEF_25-75 % by 126 ml (p = 0.012) and FEF_25-75 %/FVC ratio by 3.62pp (p = 0.011). CE trajectory showed higher odds of wheezing (OR 4.14; p<0.001) and cough (OR 2.39; p = 0.002) compared to the non-exposed group.

Conclusions: The in-uterus exposure to maternal smoking reduces PF later in life. However, the perpetuation of smoking behaviour throughout adolescence and early adulthood is determinant for PF main reduction and the emergence of respiratory-related symptoms.