The 'dawn phenomenon': What causes it?

What is the "dawn phenomenon" that some people with diabetes experience? Can anything be done about it?

- Ken / No state given

Mayo Clinic endocrinologist Maria Collazo-Clavell, M.D., and colleagues answer select questions from readers.

Answer

The "dawn effect," also called the "dawn phenomenon," is the term used to describe an abnormal early-morning increase in blood sugar (glucose) — usually between 4 a.m. and 8 a.m. — in people with diabetes. The dawn phenomenon is more common in people with type 1 diabetes than in those with type 2 diabetes.

The exact cause of the dawn phenomenon isn't known. Some researchers believe it's due to the natural overnight release of hormones — including growth hormones, cortisol, glucagon and epinephrine — that increase insulin resistance.

High morning blood sugar may also have other causes. Insufficient insulin the night before, incorrect medication dosages or eating carbohydrate snacks at bedtime may cause blood sugar to be elevated in the morning. Checking your blood sugars throughout the night will help you and your doctor to determine if you have the dawn phenomenon or if there's another reason for an elevated morning blood sugar reading.

Based on the results of blood testing throughout the night, your doctor may recommend one of the following options to prevent or correct high blood sugar levels in the morning: