Body mass index trajectories from birth to adolescence and their association with asthma: a longitudinal study of the Leicester Respiratory Cohorts

INTRODUCTION: Asthma has been associated with obesity in both adults and children. We investigated the association between longitudinal BMI trajectories and asthma at ages 8-9, 12-13, and 16-17 years in a UK cohort of White and South Asian children and adolescents. METHODS: We analysed data from the Leicester Respiratory Cohorts, population-based cohort studies that recruited 0-4-year-old children in 1990 (N = 1650) and 1998 (N = 8700) and followed them up until 2010. Outcome data on asthma came from postal questionnaires throughout infancy, childhood, and adolescence. BMI data came from birth records, well-child visits, questionnaires, and a clinical study visit. We used Group-based trajectory modelling to identify distinct BMI trajectories and used multivariable logistic regression to investigate the association with asthma. RESULTS: Out of 10,350 participants in the Leicester Respiratory Cohorts, we were able to model BMI trajectories for 5571 (54%); 1801 (17%) had information on asthma at 8-9 years of age, 1269 (12%) at 12-13 years, and 575 (6%) at 16-17 years. We identified five BMI trajectories: stable normal BMI (47%), persistent low BMI (30%), early overweight resolving (8%), childhood onset obesity (4%) adolescent onset overweight (11%). The persistent low BMI trajectory was associated with lower odds for asthma at age 8-9 years (0.56 [0.37-0.83]) and 12-13 years (0.38 [0.22-0.63]). Early overweight resolving was very similar to the reference stable normal BMI. The childhood onset obesity trajectory was associated with higher odds for asthma at 16-17 years (5.58 [1.35-24.40]). The adolescent onset overweight trajectory was not associated with asthma. When analysed separately, boys and girls and children of European and South Asian ancestry showed similar associations. CONCLUSION: This study strengthens the current understanding of obesity as a contributing factor in asthma development and highlights that early intervention and management of overweight and obesity in childhood, to achieve a normal BMI, may prevent secondary health impairments such as asthma.