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 (FEV), forced vital capacity (FVC), forced expiratory flow at the mid expiratory phase (FEF), FEV/FVC and FEF/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 FEV/FVC (-1.77pp;  = 0.01 and -1.58 pp; <0.001 respectively) and FEF/FVC ratio (-7.27pp;  = 0.019 and -6.04pp; <0.001 respectively) compared to the NE trajectory. Lower FEV and FEF values were also related to the GAE trajectory (-68 ml;  = 0.03 and -253 ml/s <0.001 respectively). Compared to those who never smoked, individuals who smoked 10 or more cigarettes daily presented a reduction in the FEV/FVC ratio by 1.37pp (<0.001), FEF by 126 ml ( = 0.012) and FEF/FVC ratio by 3.62pp ( = 0.011). CE trajectory showed higher odds of wheezing (OR 4.14; <0.001) and cough (OR 2.39;  = 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.