C-reactive protein is associated with sleep disordered breathing independent of adiposity

It is well established that medical conditions such as obesity and cardiovascular disease are associated with increased levels of inflammatory biomarkers such as C-reactive protein (CRP). Prior studies have produced inconsistent results regarding the association between sleep disordered breathing (SDB) and CRP, possibly due to the confounding effects of obesity or medical comorbidity. The present study examined the association between degree of SDB and level of CRP independent of prevalent medical conditions and obesity. Cross-sectional study. University-based clinical sample referred for diagnostic polysomnography. The study sample consisted of 69 men (mean age 40 years; mean BMI of 31.2 kg/m2) free of prevalent medical conditions including hypertension, diabetes mellitus, and cardiovascular disease. Measurements of morning and evening CRP levels were performed along with full-montage polysomnography. Confounding due to obesity was assessed by adjustments for body mass index, waist circumference, and percent body fat. A strong association was found between degree of SDB and serum levels of CRP, with or without adjustment for age and several measures of adiposity. Between the lowest and highest quartiles of apnea-hypopnea index (AHI) the mean difference in adjusted level of CRP was 3.88 microg/ml (P < 0.001). Moreover, an independent association between serum CRP levels and nocturnal hypoxia was also observed, whereas no association was noted with parameters of sleep architecture. While more research is needed to elucidate causal pathways involving the effects of sleep-related hypoxia on low-grade systemic inflammation, the results of this study suggest that mechanisms other than adiposity per se could contribute to the inflammatory state seen in adults with SDB.