Early childhood asthma and adiposity until adolescence: A prospective birth cohort study using body fat percentage

BACKGROUND: Asthma and obesity frequently coexist in childhood, yet whether asthma predisposes to later adiposity remains underexplored, particularly using measures beyond body mass index (BMI). Considering this, we aimed to examine the association between asthma in early childhood and subsequent adiposity through adolescence, assessed using BMI and body fat percentage, and to evaluate sex-specific effects. METHODS: This prospective study included 4717 participants from the Portuguese population-based Generation XXI birth cohort. Physician-diagnosed asthma at age 4 years was the exposure. Incident obesity and overweight/obesity were assessed at ages 7-, 10-, and 13-years using BMI and body fat percentage estimated by bioelectrical impedance analysis and classified according to age- and sex-specific percentiles. Children who were already overweight or obese at age 4 were excluded from the respective analysis. Cox proportional hazards models were used to estimate hazard ratios (HR) and 95% confidence intervals (CI), adjusting for confounders. Effect modification by sex was tested, and sex-stratified analyses were performed. RESULTS: Asthma was associated with a higher risk of incident obesity defined by body fat percentage in adjusted analyses (aHR = 1.91, 95% CI: 1.16-3.16), whereas associations with BMI-defined obesity were not statistically significant. Sex-stratified analyses showed that these associations were confined to girls, who had increased risk of obesity (aHR = 1.97, 95% CI: 1.19-3.26) and overweight/obesity (aHR = 1.75, 95% CI: 1.02-3.01) defined by body fat percentage. No significant associations were observed among boys. CONCLUSIONS: Asthma in early childhood was associated with increased adiposity in adolescence assessed by body fat percentage, particularly among girls. These findings suggest that children with asthma may develop excess fat accumulation not fully captured by BMI and support the integration of body composition and metabolic risk assessment into pediatric asthma care.