It is a natural phenomenon that causes a morning rise in blood sugars caused by release of certain hormones like cortisol, glucagon etc, that further causes liver to produce glucose, which further causes a rise in blood glucose levels.

It is usually seen between 2 am to 8 am and best way to diagnose dawn phenomenon is a CGM (continuous glucose monitoring) system, where you can observe a gradual rise in blood glucose levels even after a normal level before sleeping.

It is usually attributed to the transition phase between sleep to wakefulness, which causes release of stress hormones responsible for waking up a person.

How is it different from Somogyi Effect?

It is sometimes confused with Somogyi effect, but Somogyi effect causes a morning rise in blood glucose levels as a result of nocturnal hypoglycaemia. On the contrary, Dawn phenomenon is a natural rise in blood sugar due to secretion of some stress hormones and can be seen in non-diabetic individuals also.

Dawn phenomenon is a concern in diabetics, as it develops a transient insulin resistance and can be corrected with adjustments in Insulin regime and avoiding bedtime carbohydrates.