| Summary: | Type 2 diabetes exerts a negative impact on sleep breathing. It is unknown whether a long-term improvement in glycemic control ameliorates this effect. We conducted an interventional study with 35 patients with type 2 diabetes and obstructive sleep apnea (OSA) to explore this. At home, sleep breathing parameters were assessed at baseline and after a 4-month period in which antidiabetic therapy was intensified. Patients who decreased their body mass index ≥2kg/m<sup>2</sup> were excluded. Those with an HbA1c reduction ≥0.5% were considered good responders (<i>n</i> = 24). After the follow-up, good responders exhibited an improvement in the apnea–hypopnea index (AHI: 26-1 (95% IC: 8.6–95.0) vs. 20.0 (4.0–62.4) events/hour, <i>p</i> = 0.002) and in time with oxygen saturation below 90% (CT90: 13.3 (0.4–69.0) vs. 8.1 (0.4–71.2) %, <i>p</i> = 0.002). No changes were observed in the group of non–responders (<i>p</i> = 0.722 and <i>p</i> = 0.138, respectively). The percentage of moderate and severe OSA decreased among good responders (<i>p</i> = 0.040). In the wider population, the change in HbA1c correlated positively to decreases in AHI (r = 0.358, <i>p</i> = 0.035) and negatively to increases in the minimum arterial oxygen saturation (r = −0.386, <i>p</i> = 0.039). Stepwise multivariate regression analysis showed that baseline AHI and the absolute change in HbA1c independently predicted decreased AHI (R<sup>2</sup> = 0.496). The improvement of glycemic control exerts beneficial effects on sleep breathing parameters in type 2 diabetes, which cannot be attributed merely to weight loss.
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