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Diseases & Conditions

What Causes High Blood Sugar Levels in the Morning

There are two reasons why your blood sugars levels may be high in the morning – the dawn phenomenon and the Somogyi effect.

Dawn phenomenon.

The dawn phenomenon is the end result of a combination of natural body changes that occur during the sleep cycle and can be explained as follows. Your body has little need for insulin between about midnight and about 3:00 a.m. (a time when your body is sleeping most soundly). Any insulin taken in the evening causes blood sugar levels to drop sharply during this time. Then, between 3:00 a.m. and 8:00 a.m., your body starts churning out stored glucose (sugar) to prepare for the upcoming day as well as releases hormones that reduce the body’s sensitivity to insulin. All of these events happen as your bedtime insulin dose is also wearing off. These events, taken together, cause your body’s blood sugar levels to rise in the morning (at "dawn").

Somogyi effect.

A second cause of high blood sugar levels in the morning might be due to the Somogyi effect (named after the doctor who first wrote about it). This condition is also called "rebound hyperglycemia." Although the cascade of events and end result – high blood sugar levels in the morning – is the same as in the dawn phenomenon, the cause is more "man-made" (a result of poor diabetes management) in the Somogyi effect. There are two potential causes. In one scenario, your blood sugar may drop too low in the middle of the night and then your body releases hormones to raise the sugar levels. This could happen if you took too much insulin earlier or if you did not have enough of a bedtime snack. The other scenario is when your dose of long-acting insulin at bedtime is not enough and you wake up with a high morning blood sugar.

Because the cascade of events is the same with both scenarios, how is it determined if the dawn phenomenon or Somogyi effect is causing the high blood sugar levels?

Your doctor will likely ask you to check your blood sugar levels between 2:00 a.m. and 3:00 a.m. for several nights in a row. If your blood sugar is consistently low during this time, the Somogyi effect is suspected. If the blood sugar is normal or high during this time period, the dawn phenomenon is more likely to be the cause.

How can this situation be corrected?

Once you and your doctor determine how your blood sugar levels are behaving at night, he or she can advise you about the changes you need to make to better control them. Options that your doctor may discuss include:

  • Changing the time you take the long-acting insulin in the evening so that its peak action occurs when your blood sugars start rising
  • Changing the type of insulin you take in the evening
  • Taking extra insulin overnight
  • Eating a lighter breakfast
  • Increasing your morning dose of insulin
  • Switching to an insulin pump, which can be programmed to release additional insulin in the morning

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This information is provided by the Cleveland Clinic and is not intended to replace the medical advice of your doctor or health care provider. Please consult your health care provider for advice about a specific medical condition. This document was last reviewed on: 2/20/2009…#11443