Dawn phenomenon is a term used to describe an abnormal rise in blood glucose levels during the early morning hours, typically between 4 a.m. and 8 a.m. It is more common in people with type I diabetes than those with type II diabetes.
Researchers believe the dawn phenomenon is caused by a natural release of counterregulatory hormones, which include cortisol, growth hormone and epinephrine. These hormones cause the liver to release extra glucose during the night to prepare for the day. In people without diabetes, the body secretes more insulin to balance this process. Those with diabetes, however, cannot make or use the insulin needed to offset the additional glucose. As a result, blood glucose levels rise in the early morning.