Positive airway pressure normalizes glucose metabolism in obstructive sleep apnea independent of diabetes and obesity

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The relationship among obstructive sleep apnea syndrome (OSAS), type 2 diabetes mellitus (DM2) and obesity is very complex and multi-directional. Obesity and increased visceral fat are important perpetuating factors for DM2 in patients with OSAS. On the other hand, OSAS itself leads to obesity by causing both leptin and insulin resistance as a consequence of activation of the sympathetic nervous system. Risk for developing DM2 further increases in patients with OSAS and obesity. Data regarding effects of positive airway pressure (PAP) therapy, gold standard treatment for OSAS, on glycemic control were inconsistent due to variability in duration of and adherence to PAP therapy. In our cohort study we investigated effects of PAP treatment on glucose metabolism in normal-weighted non-diabetic OSAS patients, in obese non-diabetic OSAS patients, and in OSAS patients with DM2. We prospectively analyzed 67 patients diagnosed with OSAS and documented to be effectively treated with PAP therapy for three months. Apnea-hypopnea index was highest in the diabetic group, being significantly higher than in the normal-weighted group (p=0.021). Mean HOMA values were significantly higher in obese (p=0.002) and diabetic group (p=0.001) than normal-weighted group; the differences were still significant after PAP therapy. HbA1c levels were significantly higher in diabetic group compared to those in normal-weighted (p=0.012) and obese (p=0.001) groups. After PAP treatment, decrease in HbA1c levels were significant in normal-weighted (p=0.008), obese (p=0.034), and diabetic (p=0.011) groups. There was no correlation with the change in HbA1c levels and age (p=0.212), BMI (p=0.322), AHI (p=0.098) or oxygen levels (p=0.122). Our study showed that treatment of OSAS by PAP therapy offers beneficial effect on glucose metabolism, not only in diabetic patients, but also in obese and normal-weighted OSAS patients. Although data regarding overall effects of PAP therapy on glycemic control present contradictory results in the literature, it should be emphasized that duration and adherence to PAP therapy were main determinants for beneficial outcome of treatment.