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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The dawn phenomenon and the Somogyi effect increase fasting (aka morning) blood glucose levels for people with diabetes, but for different reasons. Both occurrences 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. 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. But,if you've noticed a pattern of elevated blood sugars in the morning, it could be a result of the dawn phenomenon or the Somogyi effect. Find out what causes this hormonal hyperglycemia and how you can prevent and can treat it. 

The Dawn Phenomenon

The dawn phenomenon is caused by a surge of hormones that the body puts out in the early morning hours. 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." This happens because:

  • During the evening hours the body is making less insulin.
  • Hormones trigger the liver to put out more glucose. 
  • Lack of insulin results in a blood sugar rise in the a.m. 

The Somogyi Effect 

The Somogyi effect (or rebound hyperglycemia) results in morning high blood sugar (hyperglycemia) as a result very low blood sugar (hypoglycemia) during the night. It's a very rare phenomenon and most often occurs in people with Type 1 diabetes. It occurs: 

  • More commonly in people who take night-time insulin, as a result of taking too much;
  • Or if you are required to eat a snack before bed to keep your blood sugars stable and you skip it. 
  • The abundance of insulin in the blood and lack of glucose, causes the blood sugar to drop while you are sleeping.
  • As a result, your body releases hormones to counteract the drop, raising blood sugar levels. 

How Can You Tell the Difference? 

Most of the time the reason someone experiences the Somogyi effect is due to changes with their diabetes management routine, whereas the dawn phenomenon happens on it's own. But, the only way to differentiate between the two, it to test your blood sugar between 2 and 3 a.m., several nights in a row.

  • If your blood sugar is normal or elevated then the dawn phenomenon may be the culprit. If your blood sugar is low it is more likely to be the Somogyi effect. 
  • Check your eligibility for a continuous glucose monitor (CGM) — a small device that measures real time glucose 24 hours a day. Alarms can sound off when your blood sugar is trending high or low. 

What to Do to Counteract The Somogyi Effect

  • Make sure to have a snack before bed that consists of protein and some carbohydrate. For example: a handful of berries and a low-fat Greek yogurt or 1/2 nut butter sandwich on whole grain bread. 
  • 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. 


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View Article Sources
  • American Diabetes Association. Dawn Phenomenon. http://www.diabetes.org/living-with-diabetes/treatment-and-care/blood-glucose-control/dawn-phenomenon.html?referrer=https://www.google.com/
  • Choudhary P, Davies C, Emery CJ, Heller SR. "Do high fasting glucose levels suggest nocturnal hypoglycaemia? The Somogyi effect-more fiction than fact?" Diabet Med. 2013 Aug;30(8):914-7. doi: 10.1111/dme.12175.
  • Dinsmoor, Robert. "Somogyi Effect." Diabetesselfmanagement.com 15 Aug. 2006. Diabetes Self-Management.