The results of another study, appearing in the same issue, suggest that the hypoxic stress of sleep apnea may promote the progression of liver disease.
In the first study, Dr. Naresh M. Punjabi and Dr. Brock A. Beamer, from Johns Hopkins University School of Medicine, Baltimore, performed polysomnography, frequent glucose tolerance tests, and body composition measurements in 118 nondiabetic subjects. Seventy-nine of the subjects had sleep-disordered breathing, while 39 who did not served as controls.
Relative to controls, those with sleep-disordered breathing had reductions in insulin sensitivity, ranging from 26.7% to 43.7%, which were directly related to the severity of the disordered breathing. This finding was independent of gender, age, race, and percent body fat.
The study findings also showed that sleep-disordered breathing was associated with reductions in beta-cell function and glucose effectiveness.
The second study, conducted by Dr. Vsevolod Y. Polotsky, from Johns Hopkins University, Baltimore, and colleagues, involved 90 severely obese subjects who underwent sleep studies and a variety of laboratory tests, including measurement of liver enzymes. Liver biopsies were taken in 20 of the subjects during bariatric surgery.
Overall, 81.1% of patients had obstructive sleep apnea with a respiratory disturbance index greater than 5 events per hour.
Severe obesity was associated with elevations in C-reactive protein, the authors note.
Oxygen desaturation during apneic events was associated with increased insulin resistance. In addition, significant desaturation seemed to promote hepatic inflammation, hepatocyte ballooning, and liver fibrosis.
“We hypothesize that severe obesity per se acts as a ‘first hit’ in the progression of liver disease, inducing hepatic steatosis, whereas the presence of the chronic intermittent hypoxemia that often characterizes obstructive sleep apnea acts as a ‘second hit’. The hypoxic stress of obstructive sleep apnea may induce oxidative stress in the livers of patients with severe obesity, leading to further inflammation,” Dr. Polotsky said in statement.
Am J Respir Crit Care Med 2009;179:235-240.