Obstructive sleep apnoea syndrome (OSAS) is a common disorder in obesity. Leptin, an adipocyte-derived signalling factor, plays an important role in metabolic control. There is growing evidence that leptin regulation is altered in OSAS. Therefore, the aim of this study was to test the hypothesis that effective treatment will influence leptin levels in OSAS patients.Serum leptin levels were determined in 86 consecutive patients (aged 57.5±11.0 yrs) with polysomnographically verified OSAS. In addition, leptin levels were reassessed and treatment efficacy was evaluated by polysomnography after 6 months of therapy.Patients were treated with continuous or bilevel positive airway pressure, a mandibular advancement device or conservatively, depending on the clinical symptoms. Mean serum leptin levels did not change with treatment in the whole study group (7.3±5.0versus7.5±4.8 ng·mL−1), however, leptin levels decreased in effectively treated patients (8.5±5.0versus7.4±5.1 ng·mL−1) while they increased in ineffectively treated patients (5.0±4.0versus7.7±4.1 ng·mL−1). Furthermore, not only was there a significant and independent correlation between the change in leptin levels with treatment and the change in body mass index, but also with the change in apnoea/hypopnoea index.Effective treatment of sleep-disordered breathing may have significant effects on leptin levels in obstructive sleep apnoea syndrome patients. Changes in leptin levels are related to changes in apnoea/hypopnoea index in obstructive sleep apnoea syndrome patients.

Summary Objective Dyslipidemia is frequently observed in patients with obstructive sleep apnea syndrome (OSAS). The effects of OSAS treatment on lipid levels in these patients have been examined. 
Patients and Methods 95 consecutive patients (aged 56.6±9.5 years) with polysomnographically verified OSAS and LDL cholesterol levels of more than 130 mg per deciliter have been included in a prospective trial. Plasma total cholesterol, high‐density lipoprotein (HDL) cholesterol, low‐density lipoprotein (LDL) cholesterol, triglyceride, apolipoprotein B, and lipoprotein (a) levels were determined in all patients at baseline and after long term therapy. 
Results Total cholesterol (249.9 ± 31.4 vs. 240.0 ± 34.1 mg/dL; p = 0.01) and LDL cholesterol levels (179.4 ± 29.4 vs. 165.5 ± 32.5 mg/dL; p < 0.001) decreased significantly after 6 months in patients effectively treated, while they did not change significantly in those OSAS patients in whom treatment proved to be ineffective. Body mass index, HDL cholesterol, triglyceride, apolipoprotein B, and lipoprotein (a) levels did not change during follow‐up. Both the change of total and LDL cholesterol levels were independently associated with treatment efficacy as indicated by the change of the apnea/hypopnea index. 
Conclusion The results suggest that effective treatment of sleep‐disordered breathing may have significant effects on the total and LDL cholesterol levels in OSAS patients.