Association of metabolic factors with high-sensitivity C-reactive protein in patients with sleep-disordered breathing

Sleep-disordered breathing (SDB) such as snoring or obstructive sleep apnea and metabolic syndrome are both related to cardiovascular diseases. Being a surrogate marker of high risk for cardiovascular disorder, the high-sensitivity C-reactive protein (hs-CRP) level is thought to be elevated in patients with both SDB and metabolic syndrome. To understand better the development of cardiovascular disease in patients with SDB, we examined the association of metabolic variables with hs-CRP levels in adult patients with symptoms of SDB and without any previous treatment, who were selected to participate in the study. Metabolic parameters including fasting blood glucose, lipid profile and hs-CRP were measured following an overnight polysomnography. Laboratory and polysomnographic data were analyzed to identify variables related to high hs-CRP levels. A total of 309 patients with SDB participated in this study. Of these, 139 presented with hs-CRP < 1 mg/L and 52 presented with hs-CRP > 3 mg/L. Patients with high hs-CRP showed a higher apnea-hypopnea index (AHI), body mass index (BMI), fasting glucose, and triglyceride level, and a lower mean and minimal oxygen saturation and HDL-cholesterol level. However, ordinal regression analysis demonstrated that only a higher BMI and fasting glucose level and a lower HDL-cholesterol level were independent risk factors for cardiovascular diseases (OR = 1.076, 95 % CI = 1.009-1.147, p = 0.005; OR = 1.011, 95 % CI = 1.004-1.019, p = 0.008; OR = 0.966, 95 % CI = 0.947-0.984, p < 0.001, respectively). The results showed that elevated hs-CRP is common in patients with SDB but is not independently associated with the severity of SDB. Metabolic factors such as a higher BMI and fasting blood glucose and a lower HDL-cholesterol level were more strongly associated with elevated hs-CRP rather than with SDB severity, suggesting that metabolic parameters are important contributors to cardiovascular diseases and should be corrected in patients with SDB.