An abrupt increase of blood glucose level in the morning, particularly between 5 and 9 a.m., without an antecedent nighttime hypoglycemia
Dawn phenomenon is observed commonly in individuals with type 1 diabetes mellitus receiving insulin therapy. The possible cause is the release of hormones (e.g. cortisol, glucagon, or epinephrine) that act on liver to release glucose into the bloodstream.
A similar condition, the Somogyi phenomenon, leads to hyperglycemia. However, Somogyi phenomenon involves the occurrence of nighttime hypoglycemia before hyperglycemia in the morning.