The dawn phenomenon and diabetes control in treated NIDDM and IDDM patients

The effect of glycaemic control on the early morning plasma glucose rise, 'the dawn phenomenon', was assessed in two matching diabetic patient groups each comprising five NIDDM and two IDDM patients per group, who were otherwise considered to be in poor (HbA1 = 11.2 +/- 0.6%) or good (HbA1 = 7.6 +/- 0.2%) glycaemic control. Hourly plasma concentrations of glucose, insulin, glucagon, cortisol, and growth hormone were measured between 03.00 and 09.00 h. In all the poorly controlled diabetic patients the mean rise in plasma glucose between 06.00-08.00 and 03.00 h was greater than or equal to 1.0 mmol/l. In contrast, the plasma glucose increment was less than 1.0 mmol/l in the well controlled diabetics. The overnight mean insulin levels in the poor and well controlled patient groups were 19.3 +/- 0.5 and 25.0 +/- 0.6 mU/l (P less than 0.001) respectively. Glucagon, cortisol, and growth hormone levels in the early morning showed no significant differences between the two groups. The decline in plasma insulin from 03.00 to 08.00 h and mean cortisol level between 03.00 and 06.00 h were both significantly correlated with the increase in plasma glucose between 03.00 and 08.00 h. We concluded that an increase of 1.0 mmol/l or more in plasma glucose during the early morning is of clinical importance.