Abdominal adiposity and obstructive airway disease: testing insulin resistance and sleep disordered breathing mechanisms

• Main Authors: Haren Matthew T, Misan Gary, Paterson Tracey-Jayne, Ruffin Richard E, Grant Janet F, Buckley Jonathan D, Howe Peter RC, Newbury Jonathan, Taylor Anne W, McDermott Robyn A
• Format: Article
• Language: English
• Published: BMC 2012-06-01
• Series: BMC Pulmonary Medicine
• Subjects: Airway obstruction; Forced Expiratory Volume; Forced Vital Capacity; Asthma; Abdominal adiposity; Sleep disordered breathing
• Online Access: http://www.biomedcentral.com/1471-2466/12/31

<p>Abstract</p> <p>Background</p> <p>This study examined associations of abdominal adiposity with lung function, asthma symptoms and current doctor-diagnosed asthma and mediation by insulin resistance (IR) and sleep disordered breathing (SDB).</p> <p>Methods</p> <p>A random sample of 2500 households was drawn from the community of Whyalla, South Australia (The Whyalla Intergenerational Study of Health, WISH February 2008 - July 2009). Seven-hundred twenty-two randomly selected adults (≥18 years) completed clinical protocols (32.2% response rate). Lung function was measured by spirometry. Post-bronchodilator FEV₁/FVC was used to measure airway obstruction and reversibility of FEV₁ was calculated. Current asthma was defined by self-reported doctor-diagnosis and evidence of currently active asthma. Symptom scores for asthma (CASS) and SDB were calculated. Intra-abdominal fat (IAF) was estimated using dual-energy x-ray absorptiometry (DXA). IR was calculated from fasting glucose and insulin concentrations.</p> <p>Results</p> <p>The prevalence of current doctor-diagnosed asthma was 19.9% (95% CI 16.7 – 23.5%). The ratio of observed to expected cases given the age and sex distribution of the population was 2.4 (95%CI 2.1, 2.9). IAF was not associated with current doctor-diagnosed asthma, FEV₁/FVC or FEV₁ reversibility in men or women but was positively associated with CASS independent of IR and SDB in women. A 1% increase in IAF was associated with decreases of 12 mL and 20 mL in FEV₁ and FVC respectively in men, and 4 mL and 7 mL respectively in women. SDB mediated 12% and 26% of these associations respectively in men but had minimal effects in women.</p> <p>Conclusions</p> <p>In this population with an excess of doctor-diagnosed asthma, IAF was not a major factor in airway obstruction or doctor-diagnosed asthma, although women with higher IAF perceived more severe asthma symptoms which did not correlate with lower FEV₁. Higher IAF was significantly associated with lower FEV₁ and FVC and in men SDB mechanisms may contribute up to one quarter of this association.</p>