Dawn Phenomenon or Somogyi Effect? What's the Difference?

Two Reasons Your Blood Sugar Could Be Elevated in the Morning

Woman waking up in bed
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You wake up in the morning and check your blood sugar before breakfast. And it's high. Higher than it usually is in the morning. What's going on? A random elevated blood sugar could be a result of a variety of things: perhaps you ate too many carbohydrates the night before, you took less medicine than you're supposed to or you forgot to take it altogether.

Maybe you are getting sick or are very stressed? Or maybe it's none of those things, but what could be causing it to be high? If you've noticed a pattern of elevated blood sugars in the morning, it could be a result of something called the dawn phenomenon or the Somogyi effect. The dawn phenomenon and the Somogyi effect both can raise your fasting blood glucose levels in the morning, but for different reasons.

What Causes the Somogyi Effect and Dawn Phenomenon?

Both occurrences are very similar in some respects and have to do with hormones that tell the liver to release glucose into your blood stream while you sleep. The difference is why the hormones are released.

The Somogyi effect is caused by having too much insulin in the blood during the night. This can happen to people who take long-acting insulin, or if you are required to eat a snack before bed to keep your blood sugars stable and you didn't.

Because there is an abundance of insulin in the blood and not enough glucose, it causes the blood sugar to drop while you are sleeping. In response, your body releases hormones to counteract the drop. This is often referred to as "rebound hyperglycemia." The result? You wake up with a higher blood glucose that is out of target range.


The dawn phenomenon, on the other hand, is not caused by low blood sugar. Rather, the dawn phenomenon is caused by a surge of hormones that the body puts out in the early morning hours. At this time, the body is making less insulin and hormones trigger the liver to put out more glucose. Without enough insulin to counteract this, the blood sugars rise and are high in the morning. According to the American Diabetes Association, "everyone has the dawn phenomenon if they have diabetes or not. People with diabetes don't have normal insulin responses to adjust for it and that is why their blood sugars go up." 

How Can You Tell the Difference? 

  • The only way to know for sure which one might be making your morning glucose levels high is to wake up sometime between 2 and 3 a.m. for several nights in a row, and check your blood sugar. If you are low at that time, it could be the Somogyi effect. If you are normal or high, then the dawn phenomenon may be the culprit. It might not be an easy task, but can help you solve the puzzle if you've been having a hard time getting your fasting blood sugars to goal. 
  • Another option maybe to see if you are eligible for a continuous glucose monitor. A continuous glucose monitor (CGM) is a small device that measures real time glucose 24 hours a day. It can help you detect high and low blood sugars. Having this device would mean you wouldn't have to wake up at night, but insurance companies have specific criteria for eligibility which means not everyone will be covered for one. 

    What To Do To Counteract The Somogyi Effect

    • Make sure to have a snack before bed that consists of more protein than carbs.
    • Let your doctor know what is happening. He or she may change your medication or insulin dosages.

    What To Do To Counteract the Dawn Phenomenon

    • Eat dinner earlier in the evening - avoid carbohydrates late at night. 
    • Exercising in the evening may help keep morning blood sugars in a better range. 
    • Discuss with your doctor - you may need to adjust the time you take your medication or the type of medication you are taking. 

    Updated on June 29, 2016 by Barbie Cervoni MS, RD, CDE


    American Diabetes Association. Dawn Phenomenon. Accessed on-line. June 24, 2016: http://www.diabetes.org/living-with-diabetes/treatment-and-care/blood-glucose-control/dawn-phenomenon.html?referrer=https://www.google.com/