A systematic review of the effect of sleep apnea syndrome and its therapy on HbA1c in type 2 diabetes

Background Sleep apnea syndrome (SAS) emerged as a risk factor for alterations of glucose metabolism independent of other risk factors. In persons with type 2 diabetes, clinical studies suggested that SAS may be associated with a worse glycemic control. The aim of this review was to summarize the effect of SAS and its therapy with continuous positive airway pressure (CPAP) on HbA1c in persons with type 2 diabetes. Methods A systematic literature search was conducted in Embase, PubMed, and Web of Science for studies published from database inception until January 24, 2019. Two reviewers assessed identified studies and performed data extraction. Any disagreement was resolved by a third reviewer. Results Most of the cross-sectional studies reported no statistically significant difference in HbA1c between those with and without SAS and no linear relation between AHI and HbA1c. Statistically significant higher HbA1c levels in those with than in those without SAS (8.4% vs. 7.6%,p = 0.04) were reported only when the analysis was adjusted for potential confounders. An inverse linear association between lowest oxygen saturation, oxygen desaturation index, and HbA1c, independent of other confounders, was reported. Of the 13 non-randomized studies and randomized clinical trials included, 7 reported no statistically significant change of HbA1c following CPAP therapy. The results were similar when we analyzed separately non-randomized and randomized clinical trials. Conclusion Current findings suggest an effect of hypoxemia during apnea/hypopnea episodes on glycemic control and do not support any effect of CPAP on glycemic control in type 2 diabetes. PROSPERO register number CRD42019123097