Some researchers believe the natural overnight release of the so-called counter-regulatory hormones — including growth hormones, cortisol, glucagon and epinephrine — increases insulin resistance, causing blood sugar to rise. High morning blood sugar may also be caused by insufficient insulin the night before, insufficient medication dosages or carbohydrate snack consumption at bedtime.
If you have persistently elevated blood sugar in the morning, checking your blood sugar once during the night — around 2 or 3 a.m. — for several nights in a row will help you and your doctor determine if you have the dawn phenomenon or if there's another reason for an elevated morning blood sugar reading.