Impact of obstructive sleep apnea on C-peptide in type 2 diabetic patients

Objective To determine the impact of obstructive sleep apnea(OSA) on C-peptide,the major clinical indicator of islet function in patients with type 2 diabetes. Methods Polysomnography was performed and C-peptide was measured in 60 patients with type 2 diabetes. Four groups were separated according to apnea-hyponea index (AHI):20 patients in group without OSA (AHI ＜5 ),21 patients in mild OSA group (5 ≤ AHI ＜ 15 ), 12 patients in moderate OSA (15 ≤ AHI ＜ 30 )group, 7 patients in severe OSA group ( AHI ≥30). Results Severity of OSA was associated with C-peptide, after adjusting age, body mass index( BMI ), waist circumference, fasting plasma glucose, fasting insulin, years of diabetes and total sleep time. Compared with patients without OSA, the adjusted mean C-peptide decreased 0.13 nmol/L( F = 3.78,P =0.032) in mild OSA group,0. 18 nmol/L ( F = 3.16, P = 0. 048 ) in moderate OSA group, and 0.25 nmoL/L ( F = 5.32, P = 0.001 ) in severe OSA group. Conclusion In patients with type 2 diabetes, severity of OSA is associated with poorer islet function. Key words: Obstructive sleep apnea; C-peptide; Type 2 diabetes mellitus; Fasting plasma glucose