Obstructive Sleep Apnea Increases Hemoglobin A1c Levels in Individuals with Normal Glucose Tolerance as Well as in Those with Abnormal Glucose Tolerance

Objective: Although there is increasing evidence linking obstructive sleep apnea (OSA) with abnormal glucose metabolism, the association between the severity of OSA and hemoglobin A1c (HbA1c) levels has not been fully investigated. This study examined this association.
Methods: The HbA1c levels were measured in 330 subjects who were suspected of having OSA and who underwent polysomnography. A 75-g oral glucose tolerance test was performed in subjects who had not been diagnosed to have diabetes mellitus (DM). Patients using hypoglycemic agents were excluded. The 330 subjects were divided into 3 subgroups: 164 with normal glucose tolerance (NGT); 111 with impaired glucose tolerance (IGT); 55 with DM.
Results: A multiple regression analysis showed that age (standard coefficient 0.19, P = 0.001), body mass index (standard coefficient 0.14, P = 0.02), and lowest arterial oxyhemoglobin saturation (L-SpO₂) (standard coefficient -0.31, P <0.001) were associated with HbA1c in all subjects. A subgroup analysis showed that L-SpO₂ was independently associated with HbA1c in each subgroup.
Conclusions: L-SpO₂ was independently associated with HbA1c in the subjects with NGT, as well as in those with abnormal glucose tolerance (IGT or DM). These findings suggest that OSA-induced hypoxia could therefore increase an individual’s average blood glucose level.