C-reactive protein is associated with obstructive sleep apnea independent of visceral obesity.
BACKGROUND
Obstructive sleep apnea (OSA) is associated with adverse cardiovascular outcomes. C-reactive protein (CRP) predicts atherosclerotic complications. Our study evaluates whether OSA is associated with an elevated CRP level, after elimination of known confounders including visceral obesity.


METHODS
Men without significant chronic medical illness, regular medications, or illness in the preceding 4 weeks were enrolled. Subjects with morbid obesity, newly detected high BP, or fasting glucose were excluded. They underwent polysomnography and MRI of abdomen to quantify visceral fat volume. High-sensitivity CRP levels were measured.


RESULTS
111 men with mean body mass index (BMI) 26.3 +/- 3.8 kg/m(2) were evaluated. After adjustment for age, smoking, BMI, waist circumference, and sleep efficiency, CRP correlated positively with the apnea-hypopnea index (AHI) [r = 0.35, p < 0.001], duration of O(2) saturation < 90% (r = 0.29, p = 0.002), and arousal index (r = 0.32, p = 0.001), and it correlated negatively with minimal O(2) saturation (r = -0.29, p = 0.002). These correlations were consistent when adjustment was made for MRI visceral fat volume instead of waist circumference. In the regression model, significant predictors of CRP included AHI, waist circumference, and triglycerides (adjusted R(2), 0.33, p = 0.001, p = 0.002, p = 0.018, respectively). Among the 111 subjects, 32 subjects with no or mild OSA (AHI < 15 events/h) were matched with 32 subjects with moderate-to-severe OSA (AHI > or = 15 events/h) in MRI visceral fat volume. CRP was higher in subjects with moderate-to-severe OSA (median, 1.32; 0.45 to 2.34 mg/L) when compared to subjects with no or mild OSA (median, 0.54; 0.25 to 0.89 mg/L; p = 0.001).


CONCLUSIONS
In healthy middle-aged men, elevated CRP level is associated with OSA independent of visceral obesity.
Lui
Macy Mei-Sze
MM
Department of Medicine, The University of Hong Kong, Hong Kong Special Administrative Region, People's Republic of China.
Lam
Jamie Chung-Mei
JC
Department of Medicine, The University of Hong Kong, Hong Kong Special Administrative Region, People's Republic of China.
Mak
Henry Ka-Fung
HK
Department of Diagnostic Radiology, The University of Hong Kong, Hong Kong Special Administrative Region, People's Republic of China.
Xu
Aimin
A
Research Centre of Heart, Brain, Hormone and Healthy Aging, Queen Mary Hospital, The University of Hong Kong, Hong Kong Special Administrative Region, People's Republic of China.
Ooi
Clara
C
Department of Diagnostic Radiology, The University of Hong Kong, Hong Kong Special Administrative Region, People's Republic of China.
Lam
David Chi-Leung
DC
Department of Medicine, The University of Hong Kong, Hong Kong Special Administrative Region, People's Republic of China.
Mak
Judith Choi-Wo
JC
Department of Medicine, The University of Hong Kong, Hong Kong Special Administrative Region, People's Republic of China.
Khong
Pek Lan
PL
Department of Diagnostic Radiology, The University of Hong Kong, Hong Kong Special Administrative Region, People's Republic of China.
Ip
Mary Sau-Man
MS
Research Centre of Heart, Brain, Hormone and Healthy Aging, Queen Mary Hospital, The University of Hong Kong, Hong Kong Special Administrative Region, People's Republic of China. Electronic address: msmip@hkucc.hku.hk.
D000328:Adult; D015415:Biomarkers / Q000032:analysis*; D015992:Body Mass Index; D002097:C-Reactive Protein / Q000032:analysis*; D006801:Humans; D050152:Intra-Abdominal Fat; D008297:Male; D008875:Middle Aged; D012044:Regression Analysis; D012680:Sensitivity and Specificity; D020181:Sleep Apnea, Obstructive / Q000378:metabolism*; D055105:Waist Circumference
D015415:Biomarkers; D002097:C-Reactive Protein