Overweight is not a comorbidity factor during childhood asthma: the GrowthOb study.

While being overweight is a risk factor for subsequent asthma in children, the importance of body mass index (BMI) as a comorbidity factor remains debated. The aim of this study was to assess the relationships between being overweight and the characteristics of childhood asthma. The BMI, BMI z-scores and International Obesity Task Force (IOTF) grades were evaluated in asthmatic children according to atopic status, symptoms during the past 3 months, exercise breathlessness, treatment and lung function in 6-15-yr-old children with confirmed asthma. 491 asthmatic children (mean ± SD age 10.8 ± 2.6 yrs; 179 females) were prospectively enrolled. There were 78 (15.5%) overweight (IOTF grade 1) and eight (1.6%) obese (grade 2) children. The children's BMI z-scores did not differ according to atopy, exacerbation, symptom-free days or treatment. The BMI z-score correlated positively with forced vital capacity and forced expiratory volume in 1 s in females, which could be related to earlier puberty in overweight females (growth spurt with increased volumes). Compared with normal weight children, overweight and obese children had reduced lung volume ratios (functional residual capacity/total lung capacity (TLC) and residual volume/TLC), no evidence of airflow limitation and similar symptoms. In conclusion, the observed functional relationships with BMI are not specific to asthma and being overweight is not associated with significant clinical impacts on asthma during childhood.