Which statement best describes the Dawn phenomenon?

• A. Nighttime insulin desensitization causing morning hyperglycemia
• B. Nocturnal hypoglycemia with rebound hyperglycemia
• C. Elevated HbA1c
• D. Decreased hepatic glucose production

Answer: (A)

The Dawn phenomenon occurs when counterregulatory hormones rise overnight, especially growth hormone and cortisol, which increases hepatic glucose production and causes insulin resistance. This combo leads to morning hyperglycemia even with overnight insulin present. The statement that best describes this is that nighttime insulin desensitization (insulin resistance) causes morning hyperglycemia, because it captures the idea that the liver is dumping more glucose and insulin action is blunted in the predawn hours. This differs from Somogyi rebound hyperglycemia, which results from overnight hypoglycemia triggering a counterregulatory surge. Elevated HbA1c is a measurement, not the mechanism, and decreased hepatic glucose production would reduce, not raise, morning glucose. To mitigate, adjust overnight basal insulin coverage or bedtime dosing to ensure adequate insulin during the predawn hours.