Non-linear association of birth weight with lung function and risk of asthma: A population-based study

BACKGROUND: The impact of birth weight on lung function and risk of asthma remains contentious. Our aim was to investigate the specific association of birth weight with lung function and the risk of asthma in children. METHODS: We performed cross-sectional analyses of 3,295 children aged 6–15 years who participated in the 2007–2012 National Health and Nutrition Examination Survey (NHANES). After controlling for potential covariates other than gestational diabetes, maternal asthma and obesity, the linear and non-linear associations of birth weight with lung function metrics and the risk of asthma were evaluated by a generalized linear model and generalized additive model, respectively. RESULTS: We observed a non-linear association of birth weight with FEV(1) %predicted, FEV(1)/FVC %predicted and FEF(25 − 75) %predicted (P for non-linearity was 0.0069, 0.0057, and 0.0027, respectively). Further threshold effect analysis of birth weight on lung function detected the turning point for birth weight was 3.6 kg. When the birth weight was < 3.6 kg, birth weight was significantly positively associated with all pulmonary function metrics. However, negative associations were found in FEV(1) %predicted, FEV(1)/FVC %predicted and FEF(25 − 75) %predicted when the birth weight was ≥3.6 kg. These results were consistent in the stratified and sensitivity analyses. Additionally, a possible non-linear relationship was also detected between birth weight and the risk of asthma. CONCLUSION: Although not all maternal factors were accounted for, our findings provided new insight into the association of birth weight with lung function. Future studies are warranted to confirm the present findings and understand the clinical significance.