Associations Between Increased Serum Leptin Levels And The Severity Of Obstructive Sleep Apnoea Independent Of Obesity

Abstract

Introduction: Obesity is closely associated with both serum leptin levels and obstructive sleep apnoea (OSA). This study investigated the relationship between leptin levels and the severity of OSA independent of obesity. Methods: Male subjects without known past medical history undergoing diagnostic polysomnography in the sleep laboratory were recruited. Their demographics, anthropometric measurements, overnight 10-hour urine for catecholamines and fasting blood for leptin assays on waking were collected. Magnetic resonance imaging (MRI) of abdomen was performed to quantify the amount of visceral fat. Results: 78 subjects were evaluated, with a mean age of 45.4+/-9.4 years, mean body mass index (BMI) of 27+/-4.2 kg/m2, and mean apnoea-hypopnoea index (AHI) of 33.7+/-24.8. They were grouped into AHI <30 (n=39) and AHI >=30 (n=39), and matched for MRI visceral fat volume. Subjects with severe OSA had higher levels of leptin (8.9+/-5.2 vs 6.73+/-3.6 ng/ml, p=0.036), urine catecholamines (p<0.005) and systolic blood pressure (p=0.004) compared to those with mild to moderate OSA. On univariate analysis, there were significant correlations between leptin and obesity indices (BMI, waist circumference, MRI visceral fat volume), sleep parameters and urinary catecholamines. In the multiple regression models, leptin levels were associated with minimum oxygen and urine catecholamines after adjustment for obesity and age. Conclusions: Serum leptin levels were increased in severe OSA subjects, and they were associated with nocturnal hypoxemia and sympathetic activation independent of obesity.