Mayo Clinic Health Library

Question

The dawn phenomenon: What can you do?

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

Updated: 11-19-2011

Answer

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

Some researchers believe the natural overnight release of 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, incorrect 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 a.m. or 3 a.m. — for several nights in a row 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.

Your doctor may recommend a number of options to help you prevent or correct high blood sugar levels in the morning:

  • Avoid carbohydrates at bedtime
  • Adjust your dose of medication or insulin
  • Switch to a different medication
  • Adjust the time of your medication or insulin from dinnertime to bedtime
  • Use an insulin pump to administer extra insulin during early-morning hours