Effects of sleep apnea severity on glycemic control in patients with type 2 diabetes prior to continuous positive airway pressure treatment.

Obstructive sleep apnea (OSA), a highly prevalent condition, is independently associated with increased risks of developing type 2 diabetes mellitus (T2D) and metabolic syndrome. It is unclear, however, if the severity of OSA has any impact on glycemic control among patients with T2D. We therefore aimed to determine the independent association between OSA severity and glycosylated hemoglobin (HbA1c) in patients with T2D. This was an observational cross-sectional study of 52 consecutive patients attending the diabetes obesity clinic between January 2008 to February 2010 with risk factors for sleep apnea and who underwent polysomnography study. Clinical, demographic, and lifestyle data were recorded using a questionnaire. Prevalence of OSA in this clinical cohort was 58%. After adjusting for age, gender, body mass index, duration of diabetes, and insulin dose, increased severity of OSA was associated with increased HbA1c levels (P<0.014 for linear trend). A plateau effect between HbA1c and OSA severity was, however, noted from moderate to severe OSA levels. The adjusted mean values of HbA1c in each OSA category were 8.62% for none, 9.36% for mild, 10.61% for moderate, and 9.91% for severe. No significant associations were noted between liver transaminase level with OSA severity (P=0.324), between body mass index with OSA severity (P=0.278), or between HbA1c levels with the Epworth Score (a measure of daytime sleepiness) (P=0.46). Increased severity of OSA is independently associated with worsening glycemic control following adjustment of various confounders, including insulin dosage. We would hypothesize therefore that identification and treating OSA among patients with T2D may confer benefits in improving glycemic control.