Correlates of serum C-reactive protein (CRP) - No association with sleep duration or sleep disordered breathing

Study Objectives: Increasing evidence suggests that alterations in sleep duration are associated with cardiovascular disease (CVD) and mortality. Additionally, sleep disordered breathing (SDB), which is associated with disturbed nighttime sleep and hypoxemia, may be an independent risk factor for CVD. The inflammatory marker, C-reactive protein (CRP), is an important predictor of CVD. We investigated potential associations between circulating CRP, sleep duration, and SDB. Design: Cross-sectional Study. Population: Participants were 907 adults from the Wisconsin Sleep Cohort Study (WSCS). Measurements and Results: CRP was measured after overnight polysomnography. The relationships between CRP and sleep parameters were evaluated using multiple linear regression with and without controlling for age, sex, and body mass index (BMI) and other potential confounders. CRP was found to be higher for women and had a strong positive correlation with age and BMI. CRP showed a significant positive association with current smoking, waist-hip ratio (WHR), LDL-cholesterol, triglycerides, leptin, and insulin, independent of age, sex, and BMI. Significant independent negative associations for CRP were observed with HDL-cholesterol (HDL), insulin sensitivity (quantitative insulin sensitivity check index [QUICKI]), and hours of exercise. There was a significant positive association between CRP levels and the apnea-hypopnea index (AHI, the measure of SDB), but these relationships were not significant after adjustment for age, sex, and BMI. No significant association between CRP levels and measures of sleep duration (polysomnographic and self-reported) were found. Conclusion: There was no significant association between CRP levels and sleep duration. The lack of an independent association between CRP levels and SDB suggests that the reported relationship between these 2 variables may be primarily driven by their association with obesity.