A 48-year-old man with type 2 diabetes reports fasting hyperglycaemia every morning despite a bedtime basal insulin dose that produces normal glucose at midnight. No nocturnal hypoglycaemia is documented on continuous glucose monitoring. What is the underlying mechanism?

• A Nocturnal rebound following undetected hypoglycaemia driven by counter-regulatory hormones
• B Antibody-mediated binding of insulin causing erratic daytime levels
• C Delayed absorption of the evening meal carbohydrates
• D Circadian surge of growth hormone and cortisol reducing insulin sensitivity in the early morning hours ✓

Explanation

The dawn phenomenon is a physiological early-morning rise in glucose caused by circadian secretion of growth hormone, cortisol, and catecholamines, which increase hepatic glucose output and reduce insulin sensitivity. It occurs without antecedent hypoglycaemia. The Somogyi phenomenon, described in option A, is rebound hyperglycaemia after nocturnal hypoglycaemia, and the absence of documented low glucose on monitoring distinguishes it here. Management is adjusting the basal dose or timing, not reducing it.

Reference: Williams Textbook of Endocrinology, 14th ed.

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