A total of 128 individuals with type 2 diabetes underwent continuous glucose monitoring for 3 consecutive days. The dawn phenomenon was defined by three different parameters according to the previous research: (1)the absolute increase of glucose level from nocturnal nadir to prebreakfast value(∂G) above 20 mg/dl; (2)∂G above 10 mg/dl; (3)insulin requirement increased at least 20%. The participants were secondarily separated by presence/absence of a dawn phenomenon based on the definitions above. The impact on blood glucose fluctuation of different groups was assessed according to the standard deviation of blood glucose(SDBG), the area under curve above 10 mmol/L(AUC), and the mean amplitude of glycemic excursions(MAGE), etc. The frequencies of dawn phenomenon were 64.8%(∂G≥20mg/dl), 85.2%(∂G≥10 mg/dl), and 59.4%(rise in insulin requirement≥20%)respectively. The impacts on SDBG, AUC, MAGE, and MODD were without statistical difference(P>0.05) between the presence and absence of the dawn phenomenon patients when ∂G≥10 mg/dl. However, the differences reached statistical significance(P<0.05) when ∂G≥20 mg/dl and the increase in insulin requirement≥20%. Besides, the incidence of dawn phenomenon was positively correlated with HOMA-IR, HbA_1C, and free C-peptide. Dawn phenomenon is a very frequent event in type 2 diabetes and not only impacts the overall glycemic control but also exaggerates glucose fluctuation. To be clinically relevant, ∂G≥20mg/dl should be taken as the quantitative criterion of the dawn phenomenon. (Chin J Endocrinol Metab, 2016, 32: 117-120)

Diabetes mellitus, type 2; Dawn phenomenon; Incidence; Continuous glucose monitoring system; Blood glucose fluctuation