General and Organ Fat Assessed by Magnetic Resonance Imaging and Respiratory Outcomes in Childhood.

Obesity has been implicated as a pathogenic factor in asthma, but the underlying role of general and organ fat is unclear. We hypothesized that organ fat, rather than the total fat mass, increases the risk of asthma. In a population-based prospective cohort study among 5,421 children aged 10 years, we measured general fat including body mass index and fat mass index by dual-energy X-ray absorptiometry, and organ fat including subcutaneous fat index, visceral fat index, pericardial fat index, and liver fat fraction by magnetic resonance imaging. Lung function was measured by spirometry. Current asthma was assessed by questionnaire. Higher body mass index and fat mass index were associated with higher FEV (-score difference [95% confidence interval (CI)], 0.16 [0.14 to 0.19] and -score difference [95% CI], 0.06 [0.03 to 0.09] per SD score increase, respectively), higher FVC (-score difference [95% CI], 0.19 [0.17 to 0.22] and -score difference [95% CI], 0.07 [0.04 to 0.10]), and lower FEV/FVC ratio (-score difference [95% CI], -0.07 [-0.10 to -0.05] and -score difference [95% CI], -0.03 [-0.06 to -0.00]) but not with forced expiratory flow after exhaling 75% of FVC or asthma. Higher visceral fat index, independent of fat mass index, was associated with higher FVC (-score difference [95% CI], 0.07 [0.03 to 0.10]), lower FEV/FVC (-score difference [95% CI], -0.05 [-0.09 to -0.01]), and higher risk of asthma (odds ratio, 1.20; 95% CI, 1.01 to 1.43 per SD score increase). No other organ fat measures were independently associated with lung function or asthma. The obesity-asthma link is driven mainly by visceral fat, independent of total fat mass; therefore, abdominal fat might contribute to asthma development.