Study objectives: Hypoadiponectinemia is associated with cardiovascular morbidity and diabetes mellitus. We hypothesize that adiponectin may be downregulated in sleep apnea through various mechanisms, contributing to cardiometabolic risks. This study investigated the relationship between serum adiponectin and sleep disordered breathing and its potential determinants.
Design: Cross-sectional study.
Subjects and setting: Adult men without prevailing medical comorbidity from the sleep clinic in a teaching hospital.
Measurements & results: One hundred thirty-four men underwent polysomnography, with mean age of 43.9 (9.8) years, and median apnea-hypopnea index (AHI) of 17.1 (5.7, 46.6). Overnight urine samples for catecholamines and blood samples for analyses of insulin, glucose and adiponectin levels from fasting subjects were taken. Insulin resistance was estimated by homeostasis model assessment (HOMA-IR). Magnetic resonance imaging was performed to quantify the amount of abdominal visceral fat. Serum adiponectin level, adjusted for age, body mass index, and visceral fat volume, was significantly lower in subjects with severe obstructive sleep apnea (AHI > or =30) compared with those with an AHI of less than 30: 4.0 (3.1, 5.4) versus 5.4 (3.6, 7.9) microg/mL, P = 0.039. After we adjusted for adiposity, adiponectin levels remained negatively correlated with AHI (P = 0.037), arousal index (P = 0.022), HOMA-IR/fasting insulin (P < 0.001), and urinary norepinephrine and normetanephrine (P < 0.008). In a multiple stepwise regression model, the independent determinants of adiponectin after adjustment for adiposity were HOMA-IR (P < 0.001) and urinary norepinephrine and normetanephrine (P = 0.037).
Conclusions: Adiponectin was suppressed in subjects with severe obstructive sleep apnea, independent of obesity. Adiponectin levels were determined by insulin resistance and sympathetic activation, factors that may be totally or partially attributed to sleep disordered breathing.