What is the dawn phenomenon (effect) in type 2 diabetes mellitus (DM)?

Updated: Sep 27, 2021
  • Author: Romesh Khardori, MD, PhD, FACP; Chief Editor: George T Griffing, MD  more...
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The Dawn phenomenon, defined as a blood glucose increase of over 20 mg/dL occurring at the end of the night, appears to be common in type 2 diabetes. In a study of 248 noninsulin-treated patients with type 2 diabetes who underwent continuous glucose monitoring for 2 consecutive days, approximately half were found to have the dawn phenomenon. [139, 140] Patients with the dawn phenomenon had HbA1c levels and 24-hour mean glucose values that were significantly higher than in other patients, the mean differences being 4.3 mmol/mol for HbA1c (0.39%) and 12.4 mg/dL for average 24-hour glucose concentrations. Mean 24-hour glucose did not significantly differ between patients treated with diet alone and those treated with oral antihyperglycemic agents (ie, oral antidiabetic drugs did not eliminate the dawn phenomenon). [139, 140]

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