To study the preliminary pathogenesis of dawn phenomenon in patients with type 2 diabetes mellitus.

Two-hundred and sixty-four patients with type 2 diabetes had performed continuous glucose monitoring since Jan 2012 to July 2014. They were divided into two groups: patients without dawn phenomenon and patients with dawn phenomenon. Biochemical indicators including liver and kidney function, blood lipids, HbA_1C, fructosamine(FMN), adrenocorticotropic hormone and cortisol were detected in the two groups. Oral glucose tolerance test, insulin releasing test and glucagon releasing test were performed. The differences in biochemical indicators, glucose level and α-cell and β-cell function after fasting and glucose-load were compared. The correlation and regression analysis were performed between dawn phenomenon and other indicators.

The level of adrenocorticotropic hormone, cortisol, HbA_1C, FMN, the increment of fasting glucose and nocturnal nadir glucose(BG₁), the glucose increment before and after breakfast(BG₂), 24-hour mean glucose, duration above high limit, and HOMA-IR were significantly higher in patients with dawn phenomenon compared to those in patients without dawn phenomenon[(6.6±2.4)vs(4.8±1.9)pmol/L, (523.8±84.2)vs(448.2±76.9)nmol/L, (8.1±2.0)% vs (7.5±1.8)%, (0.32±0.09)vs(0.29±0.08)mmol/L, (26.2±5.8)vs(18.0±4.9)mg/dl, (39.6±8.3)vs(28.8±7.4)mg/dl, (188.5±36.2)vs(164.5±31.2)mg/dl, 29∶31(41%)vs 20∶10(28%), 4.18±0.94 vs 3.82±0.82](all P<0.05). ISI and AUC_G/AUC_I were lower in patients with dawn phenomenon than those in patients without dawn phenomenon(-4.28±0.62 vs -4.04±0.54, -0.74±0.48 vs -0.63±0.30)(all P<0.05). The level of glucagon at each time point and area under curve of glucagon were significantly higher in patients with dawn phenomenon than those in patients without. 0, 60, 180 min glucagon/insulin ratio and 0, 30, 120, 180 min glucagon/glucose ratio were significantly higher in patients with dawn phenomenon(all P<0.05). Logistic regression analysis showed that dawn phenomenon was positively related to HOMA-IR, glucagon/insulin ratio, BG₂, BG₁and cortisol(all P<0.05), and negatively related to ISI(P<0.05).

Dawn phenomenon may be associated with increased secretion of cortisol and dysfunction of islet α-cell and β-cell. (Chin J Endocrinol Metab, 2015, 31: 492-496)

Diabetes mellitus, type 2; Dawn phenomenon; Cortisol; Islet α-cell; Islet β-cell