Body mass index status and peripheral airway obstruction in school-age children: a population-based cohort study

Abstract

Background: Few large prospective studies have investigated the impact of body mass index (BMI) on lung function during childhood.

Methods: Using data collected between 2002 and 2013, we analysed associations between BMI status and lung function (assessed by spirometry) from 8 to 16 years, as well as cross-sectional associations with small airway function (impulse oscillometry) at 16 years in the BAMSE cohort (n=2889). At 16 years, cross-sectional associations with local and systemic inflammation were investigated by analysing FE_NO, blood eosinophils and neutrophils.

Results: Overweight and obesity at 8 years were associated with higher FVC, but lower FEV₁/FVC ratio at 8 and 16 years. In boys, but not girls, obesity at 8 years was associated with a further reduction in FEV₁/FVC between 8 and 16 years. In cross-sectional analyses, overweight and obesity were associated with higher frequency dependence of resistance (R_5-20) and larger area under the reactance curve (AX^0.5) at 16 years. Increased blood neutrophil counts were seen in overweight and obese girls, but not in boys. No association was found between BMI status and FE_NO. Persistent, but not transient, overweight/obesity between 8 and 16 years was associated with higher R_5-20 and AX^0.5 and lower FEV₁/FVC (-2.8% (95% CI -4.1 to -1.2) in girls and -2.7% (95% CI -4.4 to -1.1) in boys) at 16 years, compared with persistent normal weight.

Conclusion: In childhood and adolescence, overweight and obesity, particularly persistent overweight, were associated with evidence of airway obstruction, including the small airways.

Keywords: asthma epidemiology.

Figure 1

Association between BMI status (thinness (●), normal weight (♦, referent), overweight (▲) and obesity (■)) at 8 years and lung function (FEV₁ (z-scores), FVC (z-scores) and FEV₁/FVC (%)) up to 16 years. β-Coefficients and 95% CIs were estimated using mixed-effect models (n=1158 girls with 1827 observations and n=1135 boys with 1689 observations). Changes in lung function between 8 and 16 years (‘change 8–16 years’) were estimated by the interaction between BMI status and the time indicator variable. BMI, body mass index.

Figure 2

Association between overweight (includes overweight and obesity) and/or wheeze at 16 years and FEV₁/FVC (%) at 16 years (n=1015 girls and 840 boys). The point estimate represents mean difference in FEV₁/FVC compared with the reference group (children with no overweight and no wheeze) calculated by linear regression adjusted for age and height. Children with thinness are excluded.

Figure 3

Associations between overweight (includes overweight and obesity) status between 8 and 16 years and FEV₁/FVC at 16 years (n=840 girls and 720 boys). The point estimate represents mean difference in FEV₁/FVC compared with the reference group (children with normal weight at 8 and 16 years) calculated by linear regression adjusted for age and height. Children with thinness are excluded.