Fat mass not linked to lung function in children with asthma

A study suggests that the relationship between body mass and lung function in children with asthma is more nuanced than previously thought.

Findings published in Pediatric Research show that a positive relationship between lung function and body mass index (BMI) in boys was driven primarily by increases in lean mass, while fat mass had no relationship with lung function in either gender.

These results contrast with previous findings in adult patients that have shown an inverse relationship between BMI and lung function. The authors say, therefore, that body composition, and not just body mass, may be important to take into account when managing pediatric patients.

“While monitoring body weight is a simple and practical way of tracking weight change in the clinical setting, our data demonstrate that body composition measurement can reveal important information about the relationship between body weight and lung function in children,” write Lisa Wood (University of Newcastle, New South Wales, Australia) and colleagues.

They studied 21 girls (mean age 13.6 years) and 27 boys (mean age 11.9 years) with asthma who underwent dual-energy X-ray absorptiometry (DEXA) to measure body composition, as well as spirometry.

In boys, there was a significant positive correlation between BMI z-score and forced vital capacity (FVC), forced expiratory volume in 1 second (FEV₁), and total lung capacity (TLC).

But while total or thoracic fat mass had no significant relationship with these respiratory parameters, total and thoracic lean mass had moderately strong positive associations with all three.

Meanwhile, in girls, BMI z-score did not relate to any lung function parameter, but total and thoracic lean mass was significantly associated with TLC. As in boys, there was no relationship between thoracic or total fat mass and any of the respiratory variables.

“An increased BMI indicates not only increased fat mass but also increased lean mass due to the effects of overnutrition and weight bearing,” comment Wood et al.

They suggest that increased lean mass may represent increased strength of the diaphragm and chest wall to expand and contract, resulting in higher spirometry values.

“It may be hypothesized that exercise interventions targeting this region (e.g., resistance training) are needed to evaluate whether increases in lean mass, particularly thoracic lean mass, can be achieved in children with asthma, and subsequently whether this is associated with improvements in lung function,” they write.

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