The influence of body mass index on lung function growth from infancy to school age

Background Elevated body mass index (BMI) and accelerated BMI gain have been associated with impaired lung function development, but evidence from infancy to school age—a critical period with lasting effects—is limited. We examined the association between BMI and lung function growth during this period. Methods Using longitudinal data from 472 healthy infants from the prospective Basel-Bern Infant Lung Development (BILD) cohort, BMI and lung function z-scores were obtained postnatally (ratio of peak tidal expiratory flow to expiratory time [T PTEF /T E ], functional residual capacity measured by multiple breath washout [FRC MBW ]) and at six years of age (FEV 1 , FVC, FRC Pleth , FRC MBW ). Associations between BMI and lung function growth were assessed using linear mixed-effects models with a BMI×time interaction. BMI was modelled as a continuous variable and by defining three BMI trajectory groups. Findings Each standard deviation ( sd ) increase in BMI z-score was associated with a 0.26 ([–0.41, −0.11], p interaction : 0.001) and 0.30 ([–0.49, −0.11], p interaction : 0.003) smaller increase in T PTEF /T E &FEV 1 and T PTEF /T E &FVC z-scores, respectively, between the postnatal and school-age visits. Each sd higher BMI z-score was cross-sectionally associated with a 0.14 lower FRC MBW z-score ([-0.27, −0.01], p: 0.033). Children with increasing BMI trajectories, particularly those becoming overweight by school age, showed reduced lung function growth. Using the tri-ponderal mass index (TMI) instead of BMI confirmed the observed associations with larger effect sizes and revealed an additional association with reduced FRC MBW growth. Conclusion Elevated BMI and accelerated BMI gain resulting in overweight are associated with impaired lung function growth already in the first six years of life, underscoring the importance of early weight monitoring. Funding The Swiss National Science Foundation funds the BILD study.