Supplementary Material for: Circulating Leptin Concentrations in Patients with Chronic Obstructive Pulmonary Disease: A Systematic Review and Meta-Analysis

<b><i>Background:</i></b> Weight loss is a clinically important risk factor indicating a poor prognosis in chronic obstructive pulmonary disease (COPD). Leptin is an important regulator of food intake and energy expenditure. <b><i>Objectives:</i></b> To conduct a meta-analysis to determine whether the level of leptin is related to the disease status of COPD. <b><i>Methods:</i></b> Studies published before December 2012 were identified by searching PubMed, Embase and the Cochrane Database. Observational studies comparing circulating leptin levels between COPD patients and healthy controls were included. Data were independently extracted by two investigators and analyzed using Stata 12.0 software. <b><i>Results:</i></b> Ten articles were included in the meta-analysis. Circulating leptin levels were correlated with the body mass index (BMI) as well as percent fat mass in stable COPD patients. The correlation coefficient tended to be weaker during exacerbation. A positive correlation between leptin and tumor necrosis factor (TNF)-α levels was found in COPD exacerbations, while it disappeared in patients with stable disease. Most studies indicated that circulating leptin levels in stable COPD patients were not significantly different from those in healthy controls when adjusted for gender and BMI, whilst leptin levels tended to elevate in exacerbation groups. <b><i>Conclusions:</i></b> The normal regulatory mechanism of leptin is maintained in stable COPD patients despite weight loss. The additional correlation between leptin and TNF-α during exacerbations may support the closer association of leptin with changes in nutritional parameters and suggests its valuable role in the evaluation of systemic inflammatory responses in COPD patients during exacerbation, which merits further study.