Insulin resistance and other metabolic aspects of the obstructive sleep apnea syndrome.

Obstructive sleep apnea syndrome (OSAS) is usually associated with conditions known to increase insulin resistance and cardiovascular risk, such as hypertension, obesity, and diabetes. Thus, investigating whether obstructive sleep apnea itself is an independent risk factor for increased insulin resistance and whether continuous positive airway pressure treatment (CPAP) might improve insulin sensitivity brings up considerable methodological problems. Even if insulin sensitivity improves, it is hard to distinguish between an effect of CPAP treatment, e.g. in the reduction of nocturnal sympathetic activity caused by the sleep disturbance, and concomitant factors, such as weight loss. Two recent investigations were able to prove that OSAS is an independent risk factor for insulin resistance: one study in a statistical approach, the other by demonstrating a significant improvement of insulin sensitivity already two days after onset of CPAP therapy, thus clearly ruling out such confounding factors as changes in lifestyle or weight loss. However, it is still not clear if this improvement in insulin sensitivity is accompanied by an improvement in the usually elevated cardiovascular risk of patients with OSAS. Since a decrease in elevated markers of subclinical inflammation--nowadays regarded as the main culprit of cardiovascular complications and atherosclerosis--such as Interleukin-6 and C-reactive protein has been reported during CPAP therapy, and since an improvement in left ventricular function and a decrease in blood pressure were also reported under CPAP treatment, there are several good reasons to assume an improvement in metabolical function in OSAS patients due to CPAP treatment.