Absence of the dawn phenomenon in normal subjects.

The existence of the dawn phenomenon, defined as an increase in plasma glucose levels and/or insulin requirements in the early morning hours, is well established in diabetic patients but remains controversial in normal subjects. To verify whether this phenomenon occurs in normal subjects, the nocturnal profiles in plasma glucose, insulin, and C-peptide levels; insulin to glucose ratio; and prehepatic insulin production were studied at short intervals (4 and 10 min) in 10 normal men. The first part of the night was characterized by a decrease in all values and the presence of 1 or 2 postprandial fluctuations, followed by a steady state until 0800 h. The individual profiles were frequently superimposable, with rapid 8- to 14-min oscillations. These results do not indicate the existence of a dawn phenomenon in normal subjects.