General and organ fat measures and the risk of lower lung function and asthma in childhood

Background: Obesity and asthma often present together in children. Obesity has been implicated as a pathogenic factor in asthma, but underlying mechanisms remain unclear. We hypothesized that, compared to general fat, organ fat plays a greater role in the development of childhood asthma. Methods: In a population-based prospective cohort study among 5,421 children aged 10 years, we measured general fat including body mass index (BMI) and fat mass index (total fat mass/height4) by dual-energy X-ray absorptiometry, and organ fat including subcutaneous fat index (subcutaneous fat mass/height4), visceral fat index (visceral fat mass/height3), pericardial fat index (pericardial fat mass/height3) and liver fat fraction by Magnetic Resonance Imaging. Lung function was measured by spirometry and physician-diagnosed asthma by questionnaire. Results: A higher BMI and fat mass index were associated with a higher FVC (Z-score difference (95% CI): 0.19 (0.17, 0.22) and 0.07 (0.04, 0.10)) per standard deviation score increase, respectively) and FEV1 (0.16 (0.14, 0.19) and 0.06 (0.03, 0.09)), a lower FEV1/FVC ratio (-0.07 (-0.10, -0.05) and -0.03 (-0.06, -0.00)), and not with asthma. A higher visceral fat index, conditional on fat mass index, was associated with a higher FVC (0.07 (0.03, 0.10)), a lower FEV1/FVC (-0.05 (-0.09, -0.01)) and a higher risk of asthma (Odds Ratio (95%CI): 1.20 (1.01, 1.43)). No other organ fat measures were independently associated with lung function or asthma. Conclusion: The obesity-asthma link is mainly driven by visceral fat, independent of total fat mass, which implies that abdominal fat accumulation might play a role in asthma development.