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Question: What is the dawn phenomenon?
Answer: The dawn phenomenon is a sudden 10–20 mg/dl rise in blood glucose levels in the early morning hours, 3–6 a.m.1–3 It sometimes occurs in people with type 1 diabetes and rarely in people with type 2. Unlike the Somogyi effect, it is not the result of antecedent hypoglycemia.
In 1984, its frequency and reproducibility were reported in 20 patients with type 1 diabetes and 13 patients with type 2 diabetes using clamp studies.4 Plasma glucose levels increased after 6 a.m., and insulin requirements increased by at least 50% in 77% of patients with type 2 and in 75% of patients with type 1. Five patients were studied repeatedly, and coefficients of variation in individual patients were in the 4–25% range. The dawn phenomenon occurred commonly with both types of diabetes. But researchers found that its potential variability hampered efforts to adjust the patient's diabetes regimen to avert the phenomenon's occurrence.
Another study reported that the dawn phenomenon occurred in only 3% of nights when patients were on their usual regimens in the General Clinic Research Center.3 In real life situations, the dawn phenomenon was significantly less common, this study concluded.
Duration of diabetes, quality of antecedent glycemic control, state of counter-regulation to hypoglycemia, and insulin sensitivity contribute to the dawn phenomenon, according to some investigators.5,6 Other research shows that pathogenesis is due primarily to nocturnal surges in growth hormone secretion with an additional effect of the other counterregulatory hormones, including cortisol, glucagon, and epinephrine.7
HOW TO TREAT
Methods to ameliorate the dawn phenomenon include basal bolus therapy with adequate basal insulin administration before bedtime. Patients who use an insulin pump easily can increase the basal rate prior to the dawn hours.8 For those with type 2 diabetes, a regimen that controls hepatic glucose production at night with either oral agents or insulin can avert the dawn phenomenon.
I tell my pediatric patients with diabetes and their families that to treat fasting hyperglycemia, they must assess the reason for the elevation of the morning blood glucose level. This requires that they go on a fact-finding mission—either waking up multiple times at night to check blood glucose levels or wearing a continuous glucose monitor. Before treating fasting hyperglycemia, we must determine if it is due to too little insulin or other glucose-lowering medications, nocturnal hypoglycemia, or the dawn phenomenon.
If it is the dawn phenomenon, we must alter the diabetes regimen to deliver
an effective amount of glucose-lowering medication at the right time to
suppress growth and other counterregulatory hormone elevations that occur in
the early morning. Whether the dawn phenomenon is common, recurrent, severe,
and/or associated with other diabetes characteristics, in some of my patients,
it is real. 
Footnotes
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References
2. Atiea JA, Luzio S, Owens DR: The dawn phenomenon and diabetes control in treated NIDDM and IDDM patients. Diabetes Res Clin Pract 16:183–190, 1992.[Medline]
3. Carroll MF, Hardy KJ, Burge MR, et al.: Frequency of the dawn phenomenon in type 2 diabetes: Implications for diabetes therapy. Diabetes Technol Ther 4:595–605, 2002.[Medline]
4. Bolli GB, Gerich JE: The "dawn phenomenon" —a common occurrence in both non-insulin-dependent and insulin-dependent diabetes mellitus. New Engl J Med 310:746–750, 1984.[Abstract]
5. Perriello G, De Feo P, Torlone E, et al.: Nocturnal spikes of growth hormone secretion cause the dawn phenomenon in type 1 (insulin-dependent) diabetes mellitus by decreasing hepatic (and extrahepatic) sensitivity to insulin in the absence of insulin waning. Diabetologia 33:52–59, 1990.[Medline]
6. Perriello G, De Feo P, Torlone E, et al.: The dawn phenomenon in type 1 (insulin-dependent) diabetes mellitus: Magnitude, frequency, variability, and dependency on glucose counterregulation and insulin sensitivity. Diabetologia 34:21–28, 1991.[Medline]
7. Campbell PJ, Bolli GB, Cryer PE, et al.: Pathogenesis of the dawn phenomenon in patients with insulin-dependent diabetes mellitus: Accelerated glucose production and impaired glucose utilization due to nocturnal surges in growth hormone secretion. New Engl J Med 312: 1473–1479, 1985.[Abstract]
8. Kaufman FR, Halvorson M, Miller D, et al.: Insulin pump therapy in type 1 pediatric patients: Now and into the year 2000. Diabetes Metab Res Rev 15:338–352, 1999.[Medline]
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