Physical activity and body mass related to zFEV1 catch-up lung function growth in childhood: a population-based accelerated cohort study

Objective: The existence of catch-up lung function growth and its predictors is uncertain. We aimed to identify lung function trajectories and their predictors in a population-based birth cohort. Methods: We applied group-based trajectory modelling to z-scores of FEV1 and FVC from 1153 children assessed at around 4, 7, 9, 10, 11, 14, and 18 years. Multinominal logistic regression models were used to test whether pre- and postnatal potential predictors were associated with lung function trajectories. Results: We identified four lung function trajectories: a low (19% and 19% of the sample for zFEV1 and zFVC, respectively), normal (62% and 63%), and high trajectory (16% and 13%) running in parallel, and a catch-up trajectory (2% and 5%) with catch-up occurring between 4 and 10 years. For zFEV1 but not for zFVC, increased children's physical activity during early childhood was associated with the catch-up compared to the low trajectory (relative risk ratios: 1.61 per physical activity category (1.03 – 2.51)). Also for zFEV1, fewer child allergic diseases and higher body mass index z-score (zBMI) at 4 years were associated with high and normal trajectories compared to low trajectory. Similar predictors were found for the high and normal zFVC trajectories with the addition of faster zBMI growth during early childhood associated with the high compared to the low zFVC trajectory (2.70 per zBMI unit (0.99 – 7.33)). Conclusion: We found three parallel-running and one catch-up zFEV1 and zFVC trajectories, and identified physical activity, body mass and growth as predictors of zFEV1 catch-up.